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SubjectRe: [PATCH 6/6] sched/numa: Delay retrying placement for automatic NUMA balance after wake_affine
On Tue, Feb 13, 2018 at 03:01:37PM +0100, Peter Zijlstra wrote:
> On Tue, Feb 13, 2018 at 01:37:30PM +0000, Mel Gorman wrote:
> > +static void
> > +update_wa_numa_placement(struct task_struct *p, int prev_cpu, int target)
> > +{
> > + unsigned long interval;
> > +
> > + if (!static_branch_likely(&sched_numa_balancing))
> > + return;
> > +
> > + /* If balancing has no preference then continue gathering data */
> > + if (p->numa_preferred_nid == -1)
> > + return;
> > +
> > + /*
> > + * If the wakeup is not affecting locality then it is neutral from
> > + * the perspective of NUMA balacing so continue gathering data.
> > + */
> > + if (cpus_share_cache(prev_cpu, target))
> > + return;
>
> Dang, I wanted to mention this before, but it slipped my mind. The
> comment and code don't match.
>
> Did you want to write:
>
> if (cpu_to_node(prev_cpu) == cpu_to_node(target))
> return;
>

Well, it was deliberate. While it's possible to be on the same memory
node and not sharing cache, the scheduler typically is more concerned with
the LLC than NUMA per-se. If they share LLC, then I also assume that they
share memory locality.

--
Mel Gorman
SUSE Labs

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