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sched: Revert need_resched() to look at TIF_NEED_RESCHED

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Yuanhan reported a serious throughput regression in his pigz
benchmark. Using the ftrace patch I found that several idle
paths need more TLC before we can switch the generic
need_resched() over to preempt_need_resched.

The preemption paths benefit most from preempt_need_resched and
do indeed use it; all other need_resched() users don't really
care that much so reverting need_resched() back to
tif_need_resched() is the simple and safe solution.

Reported-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: lkp@linux.intel.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20130927153003.GF15690@laptop.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2013-09-27 17:30:03 +02:00 committed by Ingo Molnar
parent 1a338ac32c
commit 75f93fed50
3 changed files with 5 additions and 16 deletions
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8
arch/x86/include/asm/preempt.h
View File

@ -79,14 +79,6 @@ static __always_inline bool __preempt_count_dec_and_test(void)
GEN_UNARY_RMWcc("decl", __preempt_count, __percpu_arg(0), "e");
}
/*
* Returns true when we need to resched -- even if we can not.
*/
static __always_inline bool need_resched(void)
{
return unlikely(test_preempt_need_resched());
}
/*
* Returns true when we need to resched and can (barring IRQ state).
*/

8
include/asm-generic/preempt.h
View File

@ -84,14 +84,6 @@ static __always_inline bool __preempt_count_dec_and_test(void)
return !--*preempt_count_ptr();
}
/*
* Returns true when we need to resched -- even if we can not.
*/
static __always_inline bool need_resched(void)
{
return unlikely(test_preempt_need_resched());
}
/*
* Returns true when we need to resched and can (barring IRQ state).
*/

5
include/linux/sched.h
View File

@ -2577,6 +2577,11 @@ static inline bool __must_check current_clr_polling_and_test(void)
}
#endif
static __always_inline bool need_resched(void)
{
return unlikely(tif_need_resched());
}
/*
* Thread group CPU time accounting.
*/