linux/kernel/sched_features.h

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/*
* Disregards a certain amount of sleep time (sched_latency_ns) and
* considers the task to be running during that period. This gives it
* a service deficit on wakeup, allowing it to run sooner.
*/
SCHED_FEAT(FAIR_SLEEPERS, 1)
/*
* Only give sleepers 50% of their service deficit. This allows
* them to run sooner, but does not allow tons of sleepers to
* rip the spread apart.
*/
SCHED_FEAT(GENTLE_FAIR_SLEEPERS, 1)
/*
* By not normalizing the sleep time, heavy tasks get an effective
* longer period, and lighter task an effective shorter period they
* are considered running.
*/
SCHED_FEAT(NORMALIZED_SLEEPER, 0)
/*
* Place new tasks ahead so that they do not starve already running
* tasks
*/
SCHED_FEAT(START_DEBIT, 1)
/*
* Should wakeups try to preempt running tasks.
*/
SCHED_FEAT(WAKEUP_PREEMPT, 1)
/*
* Compute wakeup_gran based on task behaviour, clipped to
* [0, sched_wakeup_gran_ns]
*/
SCHED_FEAT(ADAPTIVE_GRAN, 1)
/*
* When converting the wakeup granularity to virtual time, do it such
* that heavier tasks preempting a lighter task have an edge.
*/
SCHED_FEAT(ASYM_GRAN, 1)
/*
* Always wakeup-preempt SYNC wakeups, see SYNC_WAKEUPS.
*/
SCHED_FEAT(WAKEUP_SYNC, 0)
/*
* Wakeup preempt based on task behaviour. Tasks that do not overlap
* don't get preempted.
*/
SCHED_FEAT(WAKEUP_OVERLAP, 0)
/*
* Use the SYNC wakeup hint, pipes and the likes use this to indicate
* the remote end is likely to consume the data we just wrote, and
* therefore has cache benefit from being placed on the same cpu, see
* also AFFINE_WAKEUPS.
*/
SCHED_FEAT(SYNC_WAKEUPS, 1)
/*
* Based on load and program behaviour, see if it makes sense to place
* a newly woken task on the same cpu as the task that woke it --
* improve cache locality. Typically used with SYNC wakeups as
* generated by pipes and the like, see also SYNC_WAKEUPS.
*/
SCHED_FEAT(AFFINE_WAKEUPS, 1)
/*
* Weaken SYNC hint based on overlap
*/
SCHED_FEAT(SYNC_LESS, 1)
/*
* Add SYNC hint based on overlap
*/
SCHED_FEAT(SYNC_MORE, 0)
/*
* Prefer to schedule the task we woke last (assuming it failed
* wakeup-preemption), since its likely going to consume data we
* touched, increases cache locality.
*/
SCHED_FEAT(NEXT_BUDDY, 0)
/*
* Prefer to schedule the task that ran last (when we did
* wake-preempt) as that likely will touch the same data, increases
* cache locality.
*/
SCHED_FEAT(LAST_BUDDY, 1)
/*
* Consider buddies to be cache hot, decreases the likelyness of a
* cache buddy being migrated away, increases cache locality.
*/
SCHED_FEAT(CACHE_HOT_BUDDY, 1)
/*
* Use arch dependent cpu power functions
*/
SCHED_FEAT(ARCH_POWER, 0)
SCHED_FEAT(HRTICK, 0)
SCHED_FEAT(DOUBLE_TICK, 0)
SCHED_FEAT(LB_BIAS, 1)
SCHED_FEAT(LB_SHARES_UPDATE, 1)
SCHED_FEAT(ASYM_EFF_LOAD, 1)
/*
* Spin-wait on mutex acquisition when the mutex owner is running on
* another cpu -- assumes that when the owner is running, it will soon
* release the lock. Decreases scheduling overhead.
*/
mutex: implement adaptive spinning Change mutex contention behaviour such that it will sometimes busy wait on acquisition - moving its behaviour closer to that of spinlocks. This concept got ported to mainline from the -rt tree, where it was originally implemented for rtmutexes by Steven Rostedt, based on work by Gregory Haskins. Testing with Ingo's test-mutex application (http://lkml.org/lkml/2006/1/8/50) gave a 345% boost for VFS scalability on my testbox: # ./test-mutex-shm V 16 10 | grep "^avg ops" avg ops/sec: 296604 # ./test-mutex-shm V 16 10 | grep "^avg ops" avg ops/sec: 85870 The key criteria for the busy wait is that the lock owner has to be running on a (different) cpu. The idea is that as long as the owner is running, there is a fair chance it'll release the lock soon, and thus we'll be better off spinning instead of blocking/scheduling. Since regular mutexes (as opposed to rtmutexes) do not atomically track the owner, we add the owner in a non-atomic fashion and deal with the races in the slowpath. Furthermore, to ease the testing of the performance impact of this new code, there is means to disable this behaviour runtime (without having to reboot the system), when scheduler debugging is enabled (CONFIG_SCHED_DEBUG=y), by issuing the following command: # echo NO_OWNER_SPIN > /debug/sched_features This command re-enables spinning again (this is also the default): # echo OWNER_SPIN > /debug/sched_features Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-01-12 13:01:47 +00:00
SCHED_FEAT(OWNER_SPIN, 1)