Re: [patch 2/2] sched: fix select_idle_sibling() logic inselect_task_rq_fair()

From: Mike Galbraith
Date: Wed Mar 10 2010 - 16:14:37 EST


On Tue, 2010-03-09 at 14:27 +0100, Mike Galbraith wrote:
> On Tue, 2010-03-09 at 07:05 +0100, Mike Galbraith wrote:
> > On Mon, 2010-03-08 at 14:24 -0800, Suresh Siddha wrote:
>
> > > Ok. I dropped that part in v2 patches that I just posted.
> >
> > Yeah, I see mails (ramble ramble) crossed in the night. I'll take them
> > out for a spin, see if your box can get fixed up without busting mine :)
>
...

BTW, does the below also cure your netbook's woes? (should)


sched: fix select_idle_sibling()

Don't bother with selection when the current cpu is idle. Recent load
balancing changes also make it no longer necessary to check wake_affine()
success before returning the selected sibling, so we now always use it.

Signed-off-by: Mike Galbraith <efault@xxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
LKML-Reference: <new-submission>

---
kernel/sched_fair.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)

Index: linux-2.6/kernel/sched_fair.c
===================================================================
--- linux-2.6.orig/kernel/sched_fair.c
+++ linux-2.6/kernel/sched_fair.c
@@ -1438,7 +1438,7 @@ static int select_task_rq_fair(struct ta
int cpu = smp_processor_id();
int prev_cpu = task_cpu(p);
int new_cpu = cpu;
- int want_affine = 0;
+ int want_affine = 0, cpu_idle = !current->pid;
int want_sd = 1;
int sync = wake_flags & WF_SYNC;

@@ -1496,13 +1496,15 @@ static int select_task_rq_fair(struct ta
* If there's an idle sibling in this domain, make that
* the wake_affine target instead of the current cpu.
*/
- if (tmp->flags & SD_SHARE_PKG_RESOURCES)
+ if (!cpu_idle && tmp->flags & SD_SHARE_PKG_RESOURCES)
target = select_idle_sibling(p, tmp, target);

if (target >= 0) {
if (tmp->flags & SD_WAKE_AFFINE) {
affine_sd = tmp;
want_affine = 0;
+ if (target != cpu)
+ cpu_idle = 1;
}
cpu = target;
}
@@ -1518,6 +1520,7 @@ static int select_task_rq_fair(struct ta
sd = tmp;
}

+#ifdef CONFIG_FAIR_GROUP_SCHED
if (sched_feat(LB_SHARES_UPDATE)) {
/*
* Pick the largest domain to update shares over
@@ -1531,9 +1534,12 @@ static int select_task_rq_fair(struct ta
if (tmp)
update_shares(tmp);
}
+#endif

- if (affine_sd && wake_affine(affine_sd, p, sync))
- return cpu;
+ if (affine_sd) {
+ if (cpu_idle || cpu == prev_cpu || wake_affine(affine_sd, p, sync))
+ return cpu;
+ }

while (sd) {
int load_idx = sd->forkexec_idx;


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