Subject: sched: Revert need_resched() to look at TIF_NEED_RESCHED From: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Date: Fri Sep 27 17:20:30 CEST 2013 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@xxxxxxxxxxxxxxx> Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx> --- arch/x86/include/asm/preempt.h | 8 -------- include/asm-generic/preempt.h | 8 -------- include/linux/sched.h | 5 +++++ 3 files changed, 5 insertions(+), 16 deletions(-) --- a/arch/x86/include/asm/preempt.h +++ b/arch/x86/include/asm/preempt.h @@ -80,14 +80,6 @@ static __always_inline bool __preempt_co } /* - * 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). */ static __always_inline bool should_resched(void) --- a/include/asm-generic/preempt.h +++ b/include/asm-generic/preempt.h @@ -85,14 +85,6 @@ static __always_inline bool __preempt_co } /* - * 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). */ static __always_inline bool should_resched(void) --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2577,6 +2577,11 @@ static inline bool __must_check current_ } #endif +static __always_inline bool need_resched(void) +{ + return unlikely(tif_need_resched()); +} + /* * Thread group CPU time accounting. */ -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html