While sending interrupts to a cpu to repeatedly wake a thread, on occasion
that thread will take a full timer tick cycle (4002 usec in my case)
to wakeup.
The problem concerns a race condition in the code around the safe_halt()
call in the default_idle() routine. Setting 'nohalt' on the kernel
command line causes the long wakeups to disappear.
void
default_idle (void)
{
local_irq_enable();
while (!need_resched()) {
--> if (can_do_pal_halt)
--> safe_halt();
else
A timer tick could arrive between the check for !need_resched and the
actual call to safe_halt() (which does a pal call to PAL_HALT_LIGHT).
By the time the timer tick completes, a thread that might now need to run
could get held up for as long as a timer tick waiting for the halted cpu.
I'm proposing that we disable irq's and check need_resched again before
calling safe_halt(). Does anyone see any problem with this approach?
Signed-off-by: Dimitri Sivanich <sivanich@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
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