When exceptions or irq are about to resume userspace, if
the task needs to be rescheduled, the arch low level code
calls schedule() directly.
If we call it, it is because we have the TIF_RESCHED flag:
- It can be set after random local calls to set_need_resched()
(RCU, drm, ...)
- A wake up happened and the CPU needs preemption. This can
happen in several ways:
* Remotely: the remote waking CPU has set TIF_RESCHED and send the
wakee an IPI to schedule the new task.
* Remotely enqueued: the remote waking CPU sends an IPI to the target
and the wake up is made by the target.
* Locally: waking CPU == wakee CPU and the wakeup is done locally.
set_need_resched() is called without IPI.
In the case of local and remotely enqueued wake ups, the tick can
be restarted when we enqueue the new task and RCU can exit the
extended quiescent state at the same time. Then by the time we reach
irq exit path and we call schedule, we are not in RCU user mode.
But if we call schedule() only because something called set_need_resched(),
RCU may still be in user mode when we reach schedule.
Also if a wake up is done remotely, the CPU might see the TIF_RESCHED
flag and call schedule while the IPI has not yet happen to restart the
tick and exit RCU user mode.
We need to manually protect against these corner cases.
Create a new API schedule_user() that calls schedule() inside
rcu_user_exit()-rcu_user_enter() in order to protect it. Archs
will need to rely on it now to implement user preemption safely.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Alessio Igor Bogani <abogani@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Avi Kivity <avi@redhat.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Gilad Ben Yossef <gilad@benyossef.com>
Cc: Hakan Akkan <hakanakkan@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Kevin Hilman <khilman@ti.com>
Cc: Max Krasnyansky <maxk@qualcomm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sven-Thorsten Dietrich <thebigcorporation@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
When an exception or an irq exits, and we are going to resume into
interrupted kernel code, the low level architecture code calls
preempt_schedule_irq() if there is a need to reschedule.
If the interrupt/exception occured between a call to rcu_user_enter()
(from syscall exit, exception exit, do_notify_resume exit, ...) and
a real resume to userspace (iret,...), preempt_schedule_irq() can be
called whereas RCU thinks we are in userspace. But preempt_schedule_irq()
is going to run kernel code and may be some RCU read side critical
section. We must exit the userspace extended quiescent state before
we call it.
To solve this, just call rcu_user_exit() in the beginning of
preempt_schedule_irq().
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Alessio Igor Bogani <abogani@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Avi Kivity <avi@redhat.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Gilad Ben Yossef <gilad@benyossef.com>
Cc: Hakan Akkan <hakanakkan@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Kevin Hilman <khilman@ti.com>
Cc: Max Krasnyansky <maxk@qualcomm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sven-Thorsten Dietrich <thebigcorporation@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Clear the syscalls hook of a task when it's scheduled out so that if
the task migrates, it doesn't run the syscall slow path on a CPU
that might not need it.
Also set the syscalls hook on the next task if needed.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Alessio Igor Bogani <abogani@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Avi Kivity <avi@redhat.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Gilad Ben Yossef <gilad@benyossef.com>
Cc: Hakan Akkan <hakanakkan@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Kevin Hilman <khilman@ti.com>
Cc: Max Krasnyansky <maxk@qualcomm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sven-Thorsten Dietrich <thebigcorporation@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Rabik and Paul reported two different issues related to the same few
lines of code.
Rabik's issue is that the nr_uninterruptible migration code is wrong in
that he sees artifacts due to this (Rabik please do expand in more
detail).
Paul's issue is that this code as it stands relies on us using
stop_machine() for unplug, we all would like to remove this assumption
so that eventually we can remove this stop_machine() usage altogether.
The only reason we'd have to migrate nr_uninterruptible is so that we
could use for_each_online_cpu() loops in favour of
for_each_possible_cpu() loops, however since nr_uninterruptible() is the
only such loop and its using possible lets not bother at all.
The problem Rabik sees is (probably) caused by the fact that by
migrating nr_uninterruptible we screw rq->calc_load_active for both rqs
involved.
So don't bother with fancy migration schemes (meaning we now have to
keep using for_each_possible_cpu()) and instead fold any nr_active delta
after we migrate all tasks away to make sure we don't have any skewed
nr_active accounting.
[ paulmck: Move call to calc_load_migration to CPU_DEAD to avoid
miscounting noted by Rakib. ]
Reported-by: Rakib Mullick <rakib.mullick@gmail.com>
Reported-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
This reverts commit 970e178985.
Nikolay Ulyanitsky reported thatthe 3.6-rc5 kernel has a 15-20%
performance drop on PostgreSQL 9.2 on his machine (running "pgbench").
Borislav Petkov was able to reproduce this, and bisected it to this
commit 970e178985 ("sched: Improve scalability via 'CPU buddies' ...")
apparently because the new single-idle-buddy model simply doesn't find
idle CPU's to reschedule on aggressively enough.
Mike Galbraith suspects that it is likely due to the user-mode spinlocks
in PostgreSQL not reacting well to preemption, but we don't really know
the details - I'll just revert the commit for now.
There are hopefully other approaches to improve scheduler scalability
without it causing these kinds of downsides.
Reported-by: Nikolay Ulyanitsky <lystor@gmail.com>
Bisected-by: Borislav Petkov <bp@alien8.de>
Acked-by: Mike Galbraith <efault@gmx.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Fix two kernel-doc warnings in kernel/sched/fair.c:
Warning(kernel/sched/fair.c:3660): Excess function parameter 'cpus' description in 'update_sg_lb_stats'
Warning(kernel/sched/fair.c:3806): Excess function parameter 'cpus' description in 'update_sd_lb_stats'
Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/50303714.3090204@xenotime.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
migrate_tasks() uses _pick_next_task_rt() to get tasks from the
real-time runqueues to be migrated. When rt_rq is throttled
_pick_next_task_rt() won't return anything, in which case
migrate_tasks() can't move all threads over and gets stuck in an
infinite loop.
Instead unthrottle rt runqueues before migrating tasks.
Additionally: move unthrottle_offline_cfs_rqs() to rq_offline_fair()
Signed-off-by: Peter Boonstoppel <pboonstoppel@nvidia.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Turner <pjt@google.com>
Link: http://lkml.kernel.org/r/5FBF8E85CA34454794F0F7ECBA79798F379D3648B7@HQMAIL04.nvidia.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Rabik and Paul reported two different issues related to the same few
lines of code.
Rabik's issue is that the nr_uninterruptible migration code is wrong in
that he sees artifacts due to this (Rabik please do expand in more
detail).
Paul's issue is that this code as it stands relies on us using
stop_machine() for unplug, we all would like to remove this assumption
so that eventually we can remove this stop_machine() usage altogether.
The only reason we'd have to migrate nr_uninterruptible is so that we
could use for_each_online_cpu() loops in favour of
for_each_possible_cpu() loops, however since nr_uninterruptible() is the
only such loop and its using possible lets not bother at all.
The problem Rabik sees is (probably) caused by the fact that by
migrating nr_uninterruptible we screw rq->calc_load_active for both rqs
involved.
So don't bother with fancy migration schemes (meaning we now have to
keep using for_each_possible_cpu()) and instead fold any nr_active delta
after we migrate all tasks away to make sure we don't have any skewed
nr_active accounting.
Reported-by: Rakib Mullick <rakib.mullick@gmail.com>
Reported-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1345454817.23018.27.camel@twins
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Pull scheduler fixes from Ingo Molnar.
* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
sched: Fix migration thread runtime bogosity
sched,rt: fix isolated CPUs leaving root_task_group indefinitely throttled
sched,cgroup: Fix up task_groups list
sched: fix divide by zero at {thread_group,task}_times
sched, cgroup: Reduce rq->lock hold times for large cgroup hierarchies
Make stop scheduler class do the same accounting as other classes,
Migration threads can be caught in the act while doing exec balancing,
leading to the below due to use of unmaintained ->se.exec_start. The
load that triggered this particular instance was an apparently out of
control heavily threaded application that does system monitoring in
what equated to an exec bomb, with one of the VERY frequently migrated
tasks being ps.
%CPU PID USER CMD
99.3 45 root [migration/10]
97.7 53 root [migration/12]
97.0 57 root [migration/13]
90.1 49 root [migration/11]
89.6 65 root [migration/15]
88.7 17 root [migration/3]
80.4 37 root [migration/8]
78.1 41 root [migration/9]
44.2 13 root [migration/2]
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1344051854.6739.19.camel@marge.simpson.net
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Root task group bandwidth replenishment must service all CPUs, regardless of
where the timer was last started, and regardless of the isolation mechanism,
lest 'Quoth the Raven, "Nevermore"' become rt scheduling policy.
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1344326558.6968.25.camel@marge.simpson.net
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
With multiple instances of task_groups, for_each_rt_rq() is a noop,
no task groups having been added to the rt.c list instance. This
renders __enable/disable_runtime() and print_rt_stats() noop, the
user (non) visible effect being that rt task groups are missing in
/proc/sched_debug.
Signed-off-by: Mike Galbraith <efault@gmx.de>
Cc: stable@kernel.org # v3.3+
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1344308413.6846.7.camel@marge.simpson.net
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
On architectures where cputime_t is 64 bit type, is possible to trigger
divide by zero on do_div(temp, (__force u32) total) line, if total is a
non zero number but has lower 32 bit's zeroed. Removing casting is not
a good solution since some do_div() implementations do cast to u32
internally.
This problem can be triggered in practice on very long lived processes:
PID: 2331 TASK: ffff880472814b00 CPU: 2 COMMAND: "oraagent.bin"
#0 [ffff880472a51b70] machine_kexec at ffffffff8103214b
#1 [ffff880472a51bd0] crash_kexec at ffffffff810b91c2
#2 [ffff880472a51ca0] oops_end at ffffffff814f0b00
#3 [ffff880472a51cd0] die at ffffffff8100f26b
#4 [ffff880472a51d00] do_trap at ffffffff814f03f4
#5 [ffff880472a51d60] do_divide_error at ffffffff8100cfff
#6 [ffff880472a51e00] divide_error at ffffffff8100be7b
[exception RIP: thread_group_times+0x56]
RIP: ffffffff81056a16 RSP: ffff880472a51eb8 RFLAGS: 00010046
RAX: bc3572c9fe12d194 RBX: ffff880874150800 RCX: 0000000110266fad
RDX: 0000000000000000 RSI: ffff880472a51eb8 RDI: 001038ae7d9633dc
RBP: ffff880472a51ef8 R8: 00000000b10a3a64 R9: ffff880874150800
R10: 00007fcba27ab680 R11: 0000000000000202 R12: ffff880472a51f08
R13: ffff880472a51f10 R14: 0000000000000000 R15: 0000000000000007
ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
#7 [ffff880472a51f00] do_sys_times at ffffffff8108845d
#8 [ffff880472a51f40] sys_times at ffffffff81088524
#9 [ffff880472a51f80] system_call_fastpath at ffffffff8100b0f2
RIP: 0000003808caac3a RSP: 00007fcba27ab6d8 RFLAGS: 00000202
RAX: 0000000000000064 RBX: ffffffff8100b0f2 RCX: 0000000000000000
RDX: 00007fcba27ab6e0 RSI: 000000000076d58e RDI: 00007fcba27ab6e0
RBP: 00007fcba27ab700 R8: 0000000000000020 R9: 000000000000091b
R10: 00007fcba27ab680 R11: 0000000000000202 R12: 00007fff9ca41940
R13: 0000000000000000 R14: 00007fcba27ac9c0 R15: 00007fff9ca41940
ORIG_RAX: 0000000000000064 CS: 0033 SS: 002b
Cc: stable@vger.kernel.org
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20120808092714.GA3580@redhat.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Peter Portante reported that for large cgroup hierarchies (and or on
large CPU counts) we get immense lock contention on rq->lock and stuff
stops working properly.
His workload was a ton of processes, each in their own cgroup,
everybody idling except for a sporadic wakeup once every so often.
It was found that:
schedule()
idle_balance()
load_balance()
local_irq_save()
double_rq_lock()
update_h_load()
walk_tg_tree(tg_load_down)
tg_load_down()
Results in an entire cgroup hierarchy walk under rq->lock for every
new-idle balance and since new-idle balance isn't throttled this
results in a lot of work while holding the rq->lock.
This patch does two things, it removes the work from under rq->lock
based on the good principle of race and pray which is widely employed
in the load-balancer as a whole. And secondly it throttles the
update_h_load() calculation to max once per jiffy.
I considered excluding update_h_load() for new-idle balance
all-together, but purely relying on regular balance passes to update
this data might not work out under some rare circumstances where the
new-idle busiest isn't the regular busiest for a while (unlikely, but
a nightmare to debug if someone hits it and suffers).
Cc: pjt@google.com
Cc: Larry Woodman <lwoodman@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Reported-by: Peter Portante <pportant@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/n/tip-aaarrzfpnaam7pqrekofu8a6@git.kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Pull scheduler fixes from Ingo Molnar:
"Fixes and two late cleanups"
* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
sched/cleanups: Add load balance cpumask pointer to 'struct lb_env'
sched: Fix comment about PREEMPT_ACTIVE bit location
sched: Fix minor code style issues
sched: Use task_rq_unlock() in __sched_setscheduler()
sched/numa: Add SD_PERFER_SIBLING to CPU domain
Pull perf updates from Ingo Molnar:
"The biggest changes are Intel Nehalem-EX PMU uncore support, uprobes
updates/cleanups/fixes from Oleg and diverse tooling updates (mostly
fixes) now that Arnaldo is back from vacation."
* 'perf-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (40 commits)
uprobes: __replace_page() needs munlock_vma_page()
uprobes: Rename vma_address() and make it return "unsigned long"
uprobes: Fix register_for_each_vma()->vma_address() check
uprobes: Introduce vaddr_to_offset(vma, vaddr)
uprobes: Teach build_probe_list() to consider the range
uprobes: Remove insert_vm_struct()->uprobe_mmap()
uprobes: Remove copy_vma()->uprobe_mmap()
uprobes: Fix overflow in vma_address()/find_active_uprobe()
uprobes: Suppress uprobe_munmap() from mmput()
uprobes: Uprobe_mmap/munmap needs list_for_each_entry_safe()
uprobes: Clean up and document write_opcode()->lock_page(old_page)
uprobes: Kill write_opcode()->lock_page(new_page)
uprobes: __replace_page() should not use page_address_in_vma()
uprobes: Don't recheck vma/f_mapping in write_opcode()
perf/x86: Fix missing struct before structure name
perf/x86: Fix format definition of SNB-EP uncore QPI box
perf/x86: Make bitfield unsigned
perf/x86: Fix LLC-* and node-* events on Intel SandyBridge
perf/x86: Add Intel Nehalem-EX uncore support
perf/x86: Fix typo in format definition of uncore PCU filter
...
With this patch struct ld_env will have a pointer of the load balancing
cpumask and we don't need to pass a cpumask around anymore.
Signed-off-by: Michael Wang <wangyun@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/4FFE8665.3080705@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Otherwise they can't be filtered for a defined task:
perf record -e sched:sched_switch ./foo
This command doesn't report any events without this patch.
I think it isn't a security concern if someone knows who will
be executed next - this can already be observed by polling /proc
state. By default perf is disabled for non-root users in any case.
I need these events for profiling sleep times. sched_switch is used for
getting callchains and sched_stat_* is used for getting time periods.
These events are combined in user space, then it can be analyzed by
perf tools.
Signed-off-by: Andrew Vagin <avagin@openvz.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Arun Sharma <asharma@fb.com>
Link: http://lkml.kernel.org/r/1342088069-1005148-1-git-send-email-avagin@openvz.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
It seems there's no specific reason to open-code it. I guess
commit 0122ec5b02 ("sched: Add p->pi_lock to task_rq_lock()")
simply missed it. Let's be consistent with others.
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1341647342-6742-1-git-send-email-namhyung@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Stefan reported a crash on a kernel before a3e5d1091c ("sched:
Don't call task_group() too many times in set_task_rq()"), he
found the reason to be that the multiple task_group()
invocations in set_task_rq() returned different values.
Looking at all that I found a lack of serialization and plain
wrong comments.
The below tries to fix it using an extra pointer which is
updated under the appropriate scheduler locks. Its not pretty,
but I can't really see another way given how all the cgroup
stuff works.
Reported-and-tested-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1340364965.18025.71.camel@twins
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Current load balance scheme requires only one cpu in a
sched_group (balance_cpu) to look at other peer sched_groups for
imbalance and pull tasks towards itself from a busy cpu. Tasks
thus pulled by balance_cpu could later get picked up by cpus
that are in the same sched_group as that of balance_cpu.
This scheme however fails to pull tasks that are not allowed to
run on balance_cpu (but are allowed to run on other cpus in its
sched_group). That can affect fairness and in some worst case
scenarios cause starvation.
Consider a two core (2 threads/core) system running tasks as
below:
Core0 Core1
/ \ / \
C0 C1 C2 C3
| | | |
v v v v
F0 T1 F1 [idle]
T2
F0 = SCHED_FIFO task (pinned to C0)
F1 = SCHED_FIFO task (pinned to C2)
T1 = SCHED_OTHER task (pinned to C1)
T2 = SCHED_OTHER task (pinned to C1 and C2)
F1 could become a cpu hog, which will starve T2 unless C1 pulls
it. Between C0 and C1 however, C0 is required to look for
imbalance between cores, which will fail to pull T2 towards
Core0. T2 will starve eternally in this case. The same scenario
can arise in presence of non-rt tasks as well (say we replace F1
with high irq load).
We tackle this problem by having balance_cpu move pinned tasks
to one of its sibling cpus (where they can run). We first check
if load balance goal can be met by ignoring pinned tasks,
failing which we retry move_tasks() with a new env->dst_cpu.
This patch modifies load balance semantics on who can move load
towards a given cpu in a given sched_domain.
Before this patch, a given_cpu or a ilb_cpu acting on behalf of
an idle given_cpu is responsible for moving load to given_cpu.
With this patch applied, balance_cpu can in addition decide on
moving some load to a given_cpu.
There is a remote possibility that excess load could get moved
as a result of this (balance_cpu and given_cpu/ilb_cpu deciding
*independently* and at *same* time to move some load to a
given_cpu). However we should see less of such conflicting
decisions in practice and moreover subsequent load balance
cycles should correct the excess load moved to given_cpu.
Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Prashanth Nageshappa <prashanth@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/4FE06CDB.2060605@linux.vnet.ibm.com
[ minor edits ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
While load balancing, if all tasks on the source runqueue are pinned,
we retry after excluding the corresponding source cpu. However, loop counters
env.loop and env.loop_break are not reset before retrying, which can lead
to failure in moving the tasks. In this patch we reset env.loop and
env.loop_break to their inital values before we retry.
Signed-off-by: Prashanth Nageshappa <prashanth@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/4FE06EEF.2090709@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Members of 'struct lb_env' are not in appropriate order to reuse compiler
added padding on 64bit architectures. In this patch we reorder those struct
members and help reduce the size of the structure from 96 bytes to 80
bytes on 64 bit architectures.
Suggested-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Prashanth Nageshappa <prashanth@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/4FE06DDE.7000403@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Traversing an entire package is not only expensive, it also leads to tasks
bouncing all over a partially idle and possible quite large package. Fix
that up by assigning a 'buddy' CPU to try to motivate. Each buddy may try
to motivate that one other CPU, if it's busy, tough, it may then try its
SMT sibling, but that's all this optimization is allowed to cost.
Sibling cache buddies are cross-wired to prevent bouncing.
4 socket 40 core + SMT Westmere box, single 30 sec tbench runs, higher is better:
clients 1 2 4 8 16 32 64 128
..........................................................................
pre 30 41 118 645 3769 6214 12233 14312
post 299 603 1211 2418 4697 6847 11606 14557
A nice increase in performance.
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1339471112.7352.32.camel@marge.simpson.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Separate out the cpuset related handling for CPU/Memory online/offline.
This also helps us exploit the most obvious and basic level of optimization
that any notification mechanism (CPU/Mem online/offline) has to offer us:
"We *know* why we have been invoked. So stop pretending that we are lost,
and do only the necessary amount of processing!".
And while at it, rename scan_for_empty_cpusets() to
scan_cpusets_upon_hotplug(), which is more appropriate considering how
it is restructured.
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20120524141650.3692.48637.stgit@srivatsabhat.in.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
In the event of CPU hotplug, the kernel modifies the cpusets' cpus_allowed
masks as and when necessary to ensure that the tasks belonging to the cpusets
have some place (online CPUs) to run on. And regular CPU hotplug is
destructive in the sense that the kernel doesn't remember the original cpuset
configurations set by the user, across hotplug operations.
However, suspend/resume (which uses CPU hotplug) is a special case in which
the kernel has the responsibility to restore the system (during resume), to
exactly the same state it was in before suspend.
In order to achieve that, do the following:
1. Don't modify cpusets during suspend/resume. At all.
In particular, don't move the tasks from one cpuset to another, and
don't modify any cpuset's cpus_allowed mask. So, simply ignore cpusets
during the CPU hotplug operations that are carried out in the
suspend/resume path.
2. However, cpusets and sched domains are related. We just want to avoid
altering cpusets alone. So, to keep the sched domains updated, build
a single sched domain (containing all active cpus) during each of the
CPU hotplug operations carried out in s/r path, effectively ignoring
the cpusets' cpus_allowed masks.
(Since userspace is frozen while doing all this, it will go unnoticed.)
3. During the last CPU online operation during resume, build the sched
domains by looking up the (unaltered) cpusets' cpus_allowed masks.
That will bring back the system to the same original state as it was in
before suspend.
Ultimately, this will not only solve the cpuset problem related to suspend
resume (ie., restores the cpusets to exactly what it was before suspend, by
not touching it at all) but also speeds up suspend/resume because we avoid
running cpuset update code for every CPU being offlined/onlined.
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20120524141611.3692.20155.stgit@srivatsabhat.in.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Pull RCU, perf, and scheduler fixes from Ingo Molnar.
The RCU fix is a revert for an optimization that could cause deadlocks.
One of the scheduler commits (164c33c6ad "sched: Fix fork() error path
to not crash") is correct but not complete (some architectures like Tile
are not covered yet) - the resulting additional fixes are still WIP and
Ingo did not want to delay these pending fixes. See this thread on
lkml:
[PATCH] fork: fix error handling in dup_task()
The perf fixes are just trivial oneliners.
* 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
Revert "rcu: Move PREEMPT_RCU preemption to switch_to() invocation"
* 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
perf kvm: Fix segfault with report and mixed guestmount use
perf kvm: Fix regression with guest machine creation
perf script: Fix format regression due to libtraceevent merge
ring-buffer: Fix accounting of entries when removing pages
ring-buffer: Fix crash due to uninitialized new_pages list head
* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
MAINTAINERS/sched: Update scheduler file pattern
sched/nohz: Rewrite and fix load-avg computation -- again
sched: Fix fork() error path to not crash
Thanks to Charles Wang for spotting the defects in the current code:
- If we go idle during the sample window -- after sampling, we get a
negative bias because we can negate our own sample.
- If we wake up during the sample window we get a positive bias
because we push the sample to a known active period.
So rewrite the entire nohz load-avg muck once again, now adding
copious documentation to the code.
Reported-and-tested-by: Doug Smythies <dsmythies@telus.net>
Reported-and-tested-by: Charles Wang <muming.wq@gmail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: stable@kernel.org
Link: http://lkml.kernel.org/r/1340373782.18025.74.camel@twins
[ minor edits ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This reverts commit 616c310e83.
(Move PREEMPT_RCU preemption to switch_to() invocation).
Testing by Sasha Levin <levinsasha928@gmail.com> showed that this
can result in deadlock due to invoking the scheduler when one of
the runqueue locks is held. Because this commit was simply a
performance optimization, revert it.
Reported-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Sasha Levin <levinsasha928@gmail.com>
Fix lots of new kernel-doc warnings in kernel/sched/fair.c:
Warning(kernel/sched/fair.c:3625): No description found for parameter 'env'
Warning(kernel/sched/fair.c:3625): Excess function parameter 'sd' description in 'update_sg_lb_stats'
Warning(kernel/sched/fair.c:3735): No description found for parameter 'env'
Warning(kernel/sched/fair.c:3735): Excess function parameter 'sd' description in 'update_sd_pick_busiest'
Warning(kernel/sched/fair.c:3735): Excess function parameter 'this_cpu' description in 'update_sd_pick_busiest'
.. more warnings
Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
It does not get processed because sched_domain_level_max is 0 at the
time that setup_relax_domain_level() is run.
Simply accept the value as it is, as we don't know the value of
sched_domain_level_max until sched domain construction is completed.
Fix sched_relax_domain_level in cpuset. The build_sched_domain() routine calls
the set_domain_attribute() routine prior to setting the sd->level, however,
the set_domain_attribute() routine relies on the sd->level to decide whether
idle load balancing will be off/on.
Signed-off-by: Dimitri Sivanich <sivanich@sgi.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20120605184436.GA15668@sgi.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Add some code to validate assumptions we're making and output
warnings if they are not.
If this trigger we want to know about it.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Alex Shi <lkml.alex@gmail.com>
Link: http://lkml.kernel.org/n/tip-6uc3wk5s9udxtdl9cnku0vtt@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Often when we run into mis-shapen topologies the balance iteration
fails to update the cpu power properly and we'll end up in /0 traps.
Always initialize the cpu-power to a semi-sane value so that we can
at least boot the machine, even if the load-balancer might not
function correctly.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/n/tip-3lbhyj25sr169ha7z3qht5na@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Weird topologies can lead to asymmetric domain setups. This needs
further consideration since these setups are typically non-minimal
too.
For now, make it work by adding an extra mask selecting which CPUs
are allowed to iterate up.
The topology that triggered it is the one from David Rientjes:
10 20 20 30
20 10 20 20
20 20 10 20
30 20 20 10
resulting in boxes that wouldn't even boot.
Reported-by: David Rientjes <rientjes@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/n/tip-3p86l9cuaqnxz7uxsojmz5rm@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Roland Dreier reported spurious, hard to trigger lockdep warnings
within the scheduler - without any real lockup.
This bit gives us the right clue:
> [89945.640512] [<ffffffff8103fa1a>] double_lock_balance+0x5a/0x90
> [89945.640568] [<ffffffff8104c546>] push_rt_task+0xc6/0x290
if you look at that code you'll find the double_lock_balance() in
question is the one in find_lock_lowest_rq() [yay for inlining].
Now find_lock_lowest_rq() has a bug.. it fails to use
double_unlock_balance() in one exit path, if this results in a retry in
push_rt_task() we'll call double_lock_balance() again, at which point
we'll run into said lockdep confusion.
Reported-by: Roland Dreier <roland@kernel.org>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1337282386.4281.77.camel@twins
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Commit cb83b629b ("sched/numa: Rewrite the CONFIG_NUMA sched
domain support") removed the NODE sched domain and started checking
if the node distance in SLIT table is farther than REMOTE_DISTANCE,
if so, it will lose the load balance chance at exec/fork/wake_affine
points.
But actually, even the node distance is farther than REMOTE_DISTANCE.
Modern CPUs also has QPI like connections, which ensures that memory
access is not too slow between nodes. So the above change in behavior
on NUMA machine causes a performance regression on various benchmarks:
hackbench, tbench, netperf, oltp, etc.
This patch will recover the scheduler behavior to old mode on all my
Intel platforms: NHM EP/EX, WSM EP, SNB EP/EP4S, and thus fixes the
perfromance regressions. (all of them just have 2 kinds distance, 10, 21)
Signed-off-by: Alex Shi <alex.shi@intel.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1338965571-9812-1-git-send-email-alex.shi@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
No need to have the last NULL entry.
Signed-off-by: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/4FBF29E7.5020805@ct.jp.nec.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The strings sched_feat_names are never changed.
Signed-off-by: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/4FBF29B2.9030904@ct.jp.nec.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
task_tick_rt() has an optimization to only reschedule SCHED_RR tasks
if they were the only element on their rq. However, with cgroups
a SCHED_RR task could be the only element on its per-cgroup rq but
still be competing with other SCHED_RR tasks in its parent's
cgroup. In this case, the SCHED_RR task in the child cgroup would
never yield at the end of its timeslice. If the child cgroup
rt_runtime_us was the same as the parent cgroup rt_runtime_us,
the task in the parent cgroup would starve completely.
Modify task_tick_rt() to check that the task is the only task on its
rq, and that the each of the scheduling entities of its ancestors
is also the only entity on its rq.
Signed-off-by: Colin Cross <ccross@android.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1337229266-15798-1-git-send-email-ccross@android.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Since nr_cpus_allowed is used outside of sched/rt.c and wants to be
used outside of there more, move it to a more natural site.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/n/tip-kr61f02y9brwzkh6x53pdptm@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
We could re-read rq->rt_avg after we validated it was smaller than
total, invalidating the check and resulting in an unintended negative.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: David Rientjes <rientjes@google.com>
Link: http://lkml.kernel.org/r/1337688268.9698.29.camel@twins
Signed-off-by: Ingo Molnar <mingo@kernel.org>
SD_OVERLAP exists to allow overlapping groups, overlapping groups
appear in NUMA topologies that aren't fully connected.
The typical result of not fully connected NUMA is that each cpu (or
rather node) will have different spans for a particular distance.
However due to how sched domains are traversed -- only the first cpu
in the mask goes one level up -- the next level only cares about the
spans of the cpus that went up.
Due to this two things were observed to be broken:
- build_overlap_sched_groups() -- since its possible the cpu we're
building the groups for exists in multiple (or all) groups, the
selection criteria of the first group didn't ensure there was a cpu
for which is was true that cpumask_first(span) == cpu. Thus load-
balancing would terminate.
- update_group_power() -- assumed that the cpu span of the first
group of the domain was covered by all groups of the child domain.
The above explains why this isn't true, so deal with it.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: David Rientjes <rientjes@google.com>
Link: http://lkml.kernel.org/r/1337788843.9783.14.camel@laptop
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Allocators don't appreciate it when you try and allocate memory from
offline nodes.
Reported-and-tested-by: Tony Luck <tony.luck@intel.com>
Reported-and-tested-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/n/tip-epfc1io9whb7o22bcujf31vn@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Follow up on commit 556061b00 ("sched/nohz: Fix rq->cpu_load[]
calculations") since while that fixed the busy case it regressed the
mostly idle case.
Add a callback from the nohz exit to also age the rq->cpu_load[]
array. This closes the hole where either there was no nohz load
balance pass during the nohz, or there was a 'significant' amount of
idle time between the last nohz balance and the nohz exit.
So we'll update unconditionally from the tick to not insert any
accidental 0 load periods while busy, and we try and catch up from
nohz idle balance and nohz exit. Both these are still prone to missing
a jiffy, but that has always been the case.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: pjt@google.com
Cc: Venkatesh Pallipadi <venki@google.com>
Link: http://lkml.kernel.org/n/tip-kt0trz0apodbf84ucjfdbr1a@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Pull user namespace enhancements from Eric Biederman:
"This is a course correction for the user namespace, so that we can
reach an inexpensive, maintainable, and reasonably complete
implementation.
Highlights:
- Config guards make it impossible to enable the user namespace and
code that has not been converted to be user namespace safe.
- Use of the new kuid_t type ensures the if you somehow get past the
config guards the kernel will encounter type errors if you enable
user namespaces and attempt to compile in code whose permission
checks have not been updated to be user namespace safe.
- All uids from child user namespaces are mapped into the initial
user namespace before they are processed. Removing the need to add
an additional check to see if the user namespace of the compared
uids remains the same.
- With the user namespaces compiled out the performance is as good or
better than it is today.
- For most operations absolutely nothing changes performance or
operationally with the user namespace enabled.
- The worst case performance I could come up with was timing 1
billion cache cold stat operations with the user namespace code
enabled. This went from 156s to 164s on my laptop (or 156ns to
164ns per stat operation).
- (uid_t)-1 and (gid_t)-1 are reserved as an internal error value.
Most uid/gid setting system calls treat these value specially
anyway so attempting to use -1 as a uid would likely cause
entertaining failures in userspace.
- If setuid is called with a uid that can not be mapped setuid fails.
I have looked at sendmail, login, ssh and every other program I
could think of that would call setuid and they all check for and
handle the case where setuid fails.
- If stat or a similar system call is called from a context in which
we can not map a uid we lie and return overflowuid. The LFS
experience suggests not lying and returning an error code might be
better, but the historical precedent with uids is different and I
can not think of anything that would break by lying about a uid we
can't map.
- Capabilities are localized to the current user namespace making it
safe to give the initial user in a user namespace all capabilities.
My git tree covers all of the modifications needed to convert the core
kernel and enough changes to make a system bootable to runlevel 1."
Fix up trivial conflicts due to nearby independent changes in fs/stat.c
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: (46 commits)
userns: Silence silly gcc warning.
cred: use correct cred accessor with regards to rcu read lock
userns: Convert the move_pages, and migrate_pages permission checks to use uid_eq
userns: Convert cgroup permission checks to use uid_eq
userns: Convert tmpfs to use kuid and kgid where appropriate
userns: Convert sysfs to use kgid/kuid where appropriate
userns: Convert sysctl permission checks to use kuid and kgids.
userns: Convert proc to use kuid/kgid where appropriate
userns: Convert ext4 to user kuid/kgid where appropriate
userns: Convert ext3 to use kuid/kgid where appropriate
userns: Convert ext2 to use kuid/kgid where appropriate.
userns: Convert devpts to use kuid/kgid where appropriate
userns: Convert binary formats to use kuid/kgid where appropriate
userns: Add negative depends on entries to avoid building code that is userns unsafe
userns: signal remove unnecessary map_cred_ns
userns: Teach inode_capable to understand inodes whose uids map to other namespaces.
userns: Fail exec for suid and sgid binaries with ids outside our user namespace.
userns: Convert stat to return values mapped from kuids and kgids
userns: Convert user specfied uids and gids in chown into kuids and kgid
userns: Use uid_eq gid_eq helpers when comparing kuids and kgids in the vfs
...
Pull perf fixes from Ingo Molnar:
- Leftover AMD PMU driver fix fix from the end of the v3.4
stabilization cycle.
- Late tools/perf/ changes that missed the first round:
* endianness fixes
* event parsing improvements
* libtraceevent fixes factored out from trace-cmd
* perl scripting engine fixes related to libtraceevent,
* testcase improvements
* perf inject / pipe mode fixes
* plus a kernel side fix
* 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
perf/x86: Update event scheduling constraints for AMD family 15h models
* 'perf-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
Revert "sched, perf: Use a single callback into the scheduler"
perf evlist: Show event attribute details
perf tools: Bump default sample freq to 4 kHz
perf buildid-list: Work better with pipe mode
perf tools: Fix piped mode read code
perf inject: Fix broken perf inject -b
perf tools: rename HEADER_TRACE_INFO to HEADER_TRACING_DATA
perf tools: Add union u64_swap type for swapping u64 data
perf tools: Carry perf_event_attr bitfield throught different endians
perf record: Fix documentation for branch stack sampling
perf target: Add cpu flag to sample_type if target has cpu
perf tools: Always try to build libtraceevent
perf tools: Rename libparsevent to libtraceevent in Makefile
perf script: Rename struct event to struct event_format in perl engine
perf script: Explicitly handle known default print arg type
perf tools: Add hardcoded name term for pmu events
perf tools: Separate 'mem:' event scanner bits
perf tools: Use allocated list for each parsed event
perf tools: Add support for displaying event parser debug info
perf test: Move parse event automated tests to separated object
Frederic Weisbecker