From: Mike Galbraith <umgwanakikbuti@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Josef Bacik <jbacik@fb.com>,
riel@redhat.com, mingo@redhat.com, linux-kernel@vger.kernel.org,
morten.rasmussen@arm.com, kernel-team <Kernel-team@fb.com>
Subject: Re: [patch] sched: beef up wake_wide()
Date: Thu, 09 Jul 2015 16:07:26 +0200 [thread overview]
Message-ID: <1436450846.3477.98.camel@gmail.com> (raw)
In-Reply-To: <20150709132654.GE3644@twins.programming.kicks-ass.net>
On Thu, 2015-07-09 at 15:26 +0200, Peter Zijlstra wrote:
> On Wed, Jul 08, 2015 at 08:13:46AM +0200, Mike Galbraith wrote:
> >
> > +/*
> > + * Detect 1:N waker/wakee relationship via a switching-frequency heuristic.
> > + * A waker of many should wake a different task than the one last awakened
> > + * at a frequency roughly N times higher than one of its wakees. In order
> > + * to determine whether we should let the load spread vs consolodating to
> > + * shared cache, we look for a minimum 'flip' frequency of llc_size in one
> > + * partner, and a factor of lls_size higher frequency in the other. With
> > + * both conditions met, we can be relatively sure that we are seeing a 1:N
> > + * relationship, and that load size exceeds socket size.
> > + */
> > static int wake_wide(struct task_struct *p)
> > {
> > + unsigned int waker_flips = current->wakee_flips;
> > + unsigned int wakee_flips = p->wakee_flips;
> > int factor = this_cpu_read(sd_llc_size);
> >
> > + if (waker_flips < wakee_flips)
> > + swap(waker_flips, wakee_flips);
>
> This makes the wakee/waker names useless, the end result is more like
> wakee_flips := client_flips, waker_flips := server_flips.
True, perhaps a rename is in order.
> > + if (wakee_flips < factor || waker_flips < wakee_flips * factor)
> > + return 0;
>
> I don't get the first condition... why would the client ever flip? It
> only talks to that one server.
So I was thinking too, and I initially cemented the relationship by
flipping both. However, the thing works in virgin source, ie clients do
in fact flip, so I removed that cementing based on the hard evidence.
> > @@ -5021,14 +5015,17 @@ select_task_rq_fair(struct task_struct *
> > {
> > struct sched_domain *tmp, *affine_sd = NULL, *sd = NULL;
> > int cpu = smp_processor_id();
> > + int new_cpu = prev_cpu;
> > int want_affine = 0;
> > int sync = wake_flags & WF_SYNC;
> >
> > rcu_read_lock();
> > + if (sd_flag & SD_BALANCE_WAKE) {
> > + want_affine = !wake_wide(p) && cpumask_test_cpu(cpu, tsk_cpus_allowed(p));
> > + if (!want_affine)
> > + goto select_idle;
> > + }
>
> So this preserves/makes worse the bug Morten spotted, even without
> want_affine we should still attempt SD_BALANCE_WAKE if set.
Yeah. I can redo it if you want, but it seems a shame to traverse for
nothing given we know SD_BALANCE_WAKE is so painful that nobody really
really wants to do that. One has to override the other in any case, no?
-Mike
next prev parent reply other threads:[~2015-07-09 14:07 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-27 21:22 [PATCH RESEND] sched: prefer an idle cpu vs an idle sibling for BALANCE_WAKE Josef Bacik
2015-05-28 3:46 ` Mike Galbraith
2015-05-28 9:49 ` Morten Rasmussen
2015-05-28 10:57 ` Mike Galbraith
2015-05-28 11:48 ` Morten Rasmussen
2015-05-28 11:49 ` Mike Galbraith
2015-05-28 10:21 ` Peter Zijlstra
2015-05-28 11:05 ` Peter Zijlstra
2015-05-28 14:27 ` Josef Bacik
2015-05-29 21:03 ` Josef Bacik
2015-05-30 3:55 ` Mike Galbraith
2015-06-01 19:38 ` Josef Bacik
2015-06-01 20:42 ` Peter Zijlstra
2015-06-01 21:03 ` Josef Bacik
2015-06-02 17:12 ` Josef Bacik
2015-06-03 14:12 ` Rik van Riel
2015-06-03 14:24 ` Peter Zijlstra
2015-06-03 14:49 ` Josef Bacik
2015-06-03 15:30 ` Mike Galbraith
2015-06-03 15:57 ` Josef Bacik
2015-06-03 16:53 ` Mike Galbraith
2015-06-03 17:16 ` Josef Bacik
2015-06-03 17:43 ` Mike Galbraith
2015-06-03 20:34 ` Josef Bacik
2015-06-04 4:52 ` Mike Galbraith
2015-06-01 22:15 ` Rik van Riel
2015-06-11 20:33 ` Josef Bacik
2015-06-12 3:42 ` Rik van Riel
2015-06-12 5:35 ` Mike Galbraith
2015-06-17 18:06 ` Josef Bacik
2015-06-18 0:55 ` Mike Galbraith
2015-06-18 3:46 ` Josef Bacik
2015-06-18 4:12 ` Mike Galbraith
2015-07-02 17:44 ` Josef Bacik
2015-07-03 6:40 ` Mike Galbraith
2015-07-03 9:29 ` Mike Galbraith
2015-07-04 15:57 ` Mike Galbraith
2015-07-05 7:17 ` Mike Galbraith
2015-07-06 5:13 ` Mike Galbraith
2015-07-06 14:34 ` Josef Bacik
2015-07-06 18:36 ` Mike Galbraith
2015-07-06 19:41 ` Josef Bacik
2015-07-07 4:01 ` Mike Galbraith
2015-07-07 9:43 ` [patch] " Mike Galbraith
2015-07-07 13:40 ` Josef Bacik
2015-07-07 15:24 ` Mike Galbraith
2015-07-07 17:06 ` Josef Bacik
2015-07-08 6:13 ` [patch] sched: beef up wake_wide() Mike Galbraith
2015-07-09 13:26 ` Peter Zijlstra
2015-07-09 14:07 ` Mike Galbraith [this message]
2015-07-09 14:46 ` Mike Galbraith
2015-07-10 5:19 ` Mike Galbraith
2015-07-10 13:41 ` Josef Bacik
2015-07-10 20:59 ` Josef Bacik
2015-07-11 3:11 ` Mike Galbraith
2015-07-13 13:53 ` Josef Bacik
2015-07-14 11:19 ` Peter Zijlstra
2015-07-14 13:49 ` Mike Galbraith
2015-07-14 14:07 ` Peter Zijlstra
2015-07-14 14:17 ` Mike Galbraith
2015-07-14 15:04 ` Peter Zijlstra
2015-07-14 15:39 ` Mike Galbraith
2015-07-14 16:01 ` Josef Bacik
2015-07-14 17:59 ` Mike Galbraith
2015-07-15 17:11 ` Josef Bacik
2015-08-03 17:07 ` [tip:sched/core] sched/fair: Beef " tip-bot for Mike Galbraith
2015-05-28 11:16 ` [PATCH RESEND] sched: prefer an idle cpu vs an idle sibling for BALANCE_WAKE Mike Galbraith
2015-05-28 11:49 ` Ingo Molnar
2015-05-28 12:15 ` Mike Galbraith
2015-05-28 12:19 ` Peter Zijlstra
2015-05-28 12:29 ` Ingo Molnar
2015-05-28 15:22 ` David Ahern
2015-05-28 11:55 ` Srikar Dronamraju
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