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- From e0a79f529d5ba2507486d498b25da40911d95cf6 Mon Sep 17 00:00:00 2001
- From: Mike Galbraith <bitbucket@online.de>
- Date: Mon, 28 Jan 2013 11:19:25 +0000
- Subject: sched: Fix select_idle_sibling() bouncing cow syndrome
- 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>
- ---
- diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
- index 8dbee9f..ed18c74 100644
- --- a/kernel/sched/fair.c
- +++ b/kernel/sched/fair.c
- @@ -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;
- }
- --
- cgit v0.9.1
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