sched: Fix select_idle_sibling() bouncing cow syndrome (e0a79f52) · Commits · 戴 / test

If the previous CPU is cache affine and idle, select it. The current implementation simply traverses the sd_llc domain, taking the first idle CPU encountered, which walks buddy pairs hand in hand over the package, inflicting excruciating pain. 1 tbench pair (worst case) in a 10 core + SMT package: pre 15.22 MB/sec 1 procs post 252.01 MB/sec 1 procs Signed-off-by:

Mike Galbraith <bitbucket@online.de> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Link: http://lkml.kernel.org/r/1359371965.5783.127.camel@marge.simpson.net Signed-off-by:

Ingo Molnar <mingo@kernel.org>

kernel/sched/fair.c

+7 −14

Original line number	Diff line number	Diff line
		@@ -3252,25 +3252,18 @@ find_idlest_cpu(struct sched_group group, struct task_struct p, int this_cpu)
		*/
		static int select_idle_sibling(struct task_struct *p, int target)
		{
		int cpu = smp_processor_id();
		int prev_cpu = task_cpu(p);
		struct sched_domain *sd;
		struct sched_group *sg;
		int i;
		int i = task_cpu(p);

		/*
		* If the task is going to be woken-up on this cpu and if it is
		* already idle, then it is the right target.
		*/
		if (target == cpu && idle_cpu(cpu))
		return cpu;
		if (idle_cpu(target))
		return target;

		/*
		* If the task is going to be woken-up on the cpu where it previously
		* ran and if it is currently idle, then it the right target.
		* If the prevous cpu is cache affine and idle, don't be stupid.
		*/
		if (target == prev_cpu && idle_cpu(prev_cpu))
		return prev_cpu;
		if (i != target && cpus_share_cache(i, target) && idle_cpu(i))
		return i;

		/*
		* Otherwise, iterate the domains and find an elegible idle cpu.
		@@ -3284,7 +3277,7 @@ static int select_idle_sibling(struct task_struct *p, int target)
		goto next;

		for_each_cpu(i, sched_group_cpus(sg)) {
		if (!idle_cpu(i))
		if (i == target \|\| !idle_cpu(i))
		goto next;
		}

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