From: Josef Bacik <jbacik@fb.com>
To: Mike Galbraith <umgwanakikbuti@gmail.com>,
Peter Zijlstra <peterz@infradead.org>
Cc: <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: Fri, 10 Jul 2015 16:59:30 -0400 [thread overview]
Message-ID: <55A03232.2090500@fb.com> (raw)
In-Reply-To: <1436505566.5715.50.camel@gmail.com>
On 07/10/2015 01:19 AM, Mike Galbraith wrote:
> 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:
>>> 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.
>
> I settled on master/slave plus hopefully improved comment block.
>
>>> + 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.
>
> (tightening heuristic up a bit by one means or another would be good,
> but "if it ain't broke, don't fix it" applies for this patchlet)
>
>>> @@ -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.
>
> Fixed. wake_wide() may override want_affine as before, want_affine may
> override other ->flags as before, but a surviving domain selection now
> results in a full balance instead of a select_idle_sibling() call.
>
> sched: beef up wake_wide()
>
> Josef Bacik reported that Facebook sees better performance with their
> 1:N load (1 dispatch/node, N workers/node) when carrying an old patch
> to try very hard to wake to an idle CPU. While looking at wake_wide(),
> I noticed that it doesn't pay attention to the wakeup of a many partner
> waker, returning 1 only when waking one of its many partners.
>
> Correct that, letting explicit domain flags override the heuristic.
>
> While at it, adjust task_struct bits, we don't need a 64bit counter.
>
> Signed-off-by: Mike Galbraith <umgwanakikbuti@gmail.com>
> Tested-by: Josef Bacik <jbacik@fb.com>
Not quite as awesome but still better than the baseline so we're good.
Thanks,
Josef
next prev parent reply other threads:[~2015-07-10 21:00 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
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 [this message]
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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