On Thu, Oct 15, 2015 at 09:26:44PM +0900, Byungchul Park wrote:
> On Thu, Oct 15, 2015 at 01:18:13PM +0200, Peter Zijlstra wrote:
> > On Thu, Oct 15, 2015 at 06:01:14PM +0900, byungchul.p...@lge.com wrote:
> > > From: Byungchul Park <byungchul.p...@lge.com>
> > >
> > > This patch removes a weird coupling between se->avg.last_update_time and
> > > the condition checking for migration, and introduce a new migration flag.
> > > Now, scheduler can use the flag instead of se->avg.last_update_time to
> > > check if migration already happened or not.
> >
> > Was there a problem with that coupling? This does not explain.
>
> The reason why i introduce the new flag is that 3/3 patch makes
> se->avg.last_update_time non-zero consistently, so we cannot use the
> condition "se->avg.last_update_time == 0" to check if migration has
> happened.
It would have been ever so good to have had that in the Changelog.
> > > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> > > index af6f252..66d0552 100644
> > > --- a/kernel/sched/sched.h
> > > +++ b/kernel/sched/sched.h
> > > @@ -1158,6 +1158,7 @@ static const u32 prio_to_wmult[40] = {
> > > #define ENQUEUE_WAKING 0
> > > #endif
> > > #define ENQUEUE_REPLENISH 8
> > > +#define ENQUEUE_MIGRATED 16
> >
> > Won't actually apply that..
>
> Okay, I got your concern, let me think more..
Ah, so what I means was that that hunk will not apply. I see that what I
typed did not express that as clearly as I might have wanted.
Current code looks like:
#define ENQUEUE_REPLENISH 0x08
#define ENQUEUE_RESTORE 0x10
> By the way, what do you think about the approach of 3/3 patch?
Again a wee bit of worry. I like it for 64bits as there its nearly free
and does the right thing, but on 32bit we add 2 smp_rmb() invocations
(which are not free on ARM etc..). [Note that one could rewrite that
function to require but a single rmb].
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