Messages in this thread Patch in this message | | | Subject | Re: [patch] sched: minimalist select_idle_sibling() bouncing cow syndrome fix | From | Mike Galbraith <> | Date | Mon, 28 Jan 2013 12:19:25 +0100 |
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On Mon, 2013-01-28 at 11:53 +0100, Ingo Molnar wrote: > * Mike Galbraith <bitbucket@online.de> wrote: > > > If the previous CPU is cache affine and idle, select it. > > No objections in principle - but would be nice to have a > changelog with numbers, % of improvement included and so?
Well, that like was my changelog, guess it needs improvement.
Take 2.
sched: minimalist select_idle_sibling() bouncing cow syndrome fix
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> --- kernel/sched/fair.c | 21 +++++++-------------- 1 file changed, 7 insertions(+), 14 deletions(-)
--- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3270,25 +3270,18 @@ find_idlest_cpu(struct sched_group *grou */ 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. @@ -3302,7 +3295,7 @@ static int select_idle_sibling(struct ta 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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