sched: Revert need_resched() to look at TIF_NEED_RESCHED (75f93fed) · Commits · 戴 / test

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>

arch/x86/include/asm/preempt.h

+0 −8

Original line number	Diff line number	Diff line
		@@ -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).
		*/

include/asm-generic/preempt.h

+0 −8

Original line number	Diff line number	Diff line
		@@ -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).
		*/

include/linux/sched.h

+5 −0

Original line number	Diff line number	Diff line
		@@ -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.
		*/

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