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SubjectRe: sched: Avoid SMT siblings in select_idle_sibling() if possible
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On Thu, 2011-11-17 at 16:56 +0100, Peter Zijlstra wrote:
> On Thu, 2011-11-17 at 16:38 +0100, Mike Galbraith wrote:
> > On Thu, 2011-11-17 at 02:59 +0100, Mike Galbraith wrote:
> > > On Wed, 2011-11-16 at 10:37 -0800, Suresh Siddha wrote:
> >
> > > > It should be ok. Isn't it?
> > >
> > > Nope, wasn't ok.
> >
> > Because you can't get to again: with a single E5620 package, it having
> > only SIBLING and MC domains.
> >
> > again:
> > for_each_domain(target, sd) {
> > if (!smt && (sd->flags & SD_SHARE_CPUPOWER))
> > continue;
> >
> > if (!(sd->flags & SD_SHARE_PKG_RESOURCES)) {
> > if (!smt) {
> > smt = 1;
> > goto again;
> >
>
> D'0h, indeed..
>
> Something like the below maybe, although I'm certain it all can be
> written much nicer indeed.

I'll give it a go.

Squabbling with bouncing buddies in an isolated and otherwise idle
cpuset ate my day.

> ---
> kernel/sched/fair.c | 14 ++++++++------
> 1 files changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index cd3b642..340e62e 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -2676,13 +2676,11 @@ static int select_idle_sibling(struct task_struct *p, int target)
> if (!smt && (sd->flags & SD_SHARE_CPUPOWER))
> continue;
>
> - if (!(sd->flags & SD_SHARE_PKG_RESOURCES)) {
> - if (!smt) {
> - smt = 1;
> - goto again;
> - }
> + if (smt && !(sd->flags & SD_SHARE_CPUPOWER))
> + break;
> +
> + if (!(sd->flags & SD_SHARE_PKG_RESOURCES))
> break;
> - }
>
> sg = sd->groups;
> do {
> @@ -2702,6 +2700,10 @@ static int select_idle_sibling(struct task_struct *p, int target)
> sg = sg->next;
> } while (sg != sd->groups);
> }
> + if (!smt) {
> + smt = 1;
> + goto again;
> + }
> done:
> rcu_read_unlock();
>
>
>
> --
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