Re: [regression] cross core scheduling frequency drop bisected to 0c313cb20732

From	Mike Galbraith <umgwanakikbuti@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [regression] cross core scheduling frequency drop bisected to 0c313cb20732
Date	2016-04-10 11:40 +0200
Message-ID	<rmk0y-2TM-11@gated-at.bofh.it> (permalink)
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On Sun, 2016-04-10 at 05:44 +0200, Rafael J. Wysocki wrote:
> On Sat, Apr 9, 2016 at 6:39 PM, Mike Galbraith <
> umgwanakikbuti@gmail.com> wrote:
> > 
> > Hm, setting gov=performance, and taking the average of 3 30 second
> > interval PkgWatt samples as pipe-test runs..
> > 
> > 714KHz/28.03Ws = 25.46
> > 877KHz/30.28Ws = 28.96
> > 
> > ..for pipe-test, the tradeoff look a bit more like red than green.
> 
> Well, fair enough, but that's just pipe-test, and what about the
> people who don't see the performance gain and see the energy loss,
> like Doug?

Perhaps Doug sees increased power because he's not throttling no_hz,
whereas I am, so he burns more power getting _to_ idle?  Dunno, maybe
he'll try the attached.  If it's a general case energy loser, so be it,
numbers talk, bs walks and all that ;-)

> Essentially, this trades performance gains in somewhat special
> workloads for increased energy consumption in idle.  Those workloads
> need not be run by everybody, but idle is.

Cross core scheduling is routine business, we do truckloads of that for
good reason, and lots of stuff does wakeups at high frequency.

> That said I applied the patch you're complaining about mostly because
> the commit that introduced the change in question in 4.5 claimed that
> it wouldn't affect idle power on systems with reasonably fast C1, but
> that didn't pass the reality test.  I'm not totally against restoring
> that change, but it would need to be based on very solid evidence.

Understood.  My box seems to be saying we can hug the trees hardest by
telling the CPU get work done as quickly as possible, but I don't have
much experience at tree hugging measurement.  Performance wise, tasks
talking via localhost is definitely not special.

tbench     1      2      4     8
base     752   1283   2250  3362

select_idle_sibling() off
         735   1344   2080  2884
delta   .977  1.047   .924  .857

select_idle_sibling() on, 0c313cb20732 reverted
         816   1317   2240  3388
delta  1.085  1.026   .995 1.007 vs base
delta  1.110   .979  1.076 1.174 vs off
               (^hm)

	-Mike

Thread

[regression] cross core scheduling frequency drop bisected to  0c313cb20732 Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-08 07:30 +0200
  Re: [regression] cross core scheduling frequency drop bisected to  0c313cb20732 Peter Zijlstra <peterz@infradead.org> - 2016-04-08 08:50 +0200
    Re: [regression] cross core scheduling frequency drop bisected to  0c313cb20732 Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-08 09:00 +0200
      Re: [regression] cross core scheduling frequency drop bisected to 0c313cb20732 "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-04-08 23:00 +0200
        RE: [regression] cross core scheduling frequency drop bisected to 0c313cb20732 "Doug Smythies" <dsmythies@telus.net> - 2016-04-09 00:20 +0200
          Re: [regression] cross core scheduling frequency drop bisected to  0c313cb20732 Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-09 08:50 +0200
          RE: [regression] cross core scheduling frequency drop bisected to 0c313cb20732 "Doug Smythies" <dsmythies@telus.net> - 2016-04-09 09:20 +0200
            Re: [regression] cross core scheduling frequency drop bisected to  0c313cb20732 Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-09 09:30 +0200
          Re: [regression] cross core scheduling frequency drop bisected to  0c313cb20732 Peter Zijlstra <peterz@infradead.org> - 2016-04-09 13:10 +0200
        Re: [regression] cross core scheduling frequency drop bisected to  0c313cb20732 Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-09 08:50 +0200
          Re: [regression] cross core scheduling frequency drop bisected to 0c313cb20732 "Rafael J. Wysocki" <rafael@kernel.org> - 2016-04-09 14:40 +0200
            Re: [regression] cross core scheduling frequency drop bisected to  0c313cb20732 Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-09 17:20 +0200
              Re: [regression] cross core scheduling frequency drop bisected to  0c313cb20732 Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-09 18:40 +0200
                Re: [regression] cross core scheduling frequency drop bisected to 0c313cb20732 "Rafael J. Wysocki" <rafael@kernel.org> - 2016-04-10 05:50 +0200
                RE: [regression] cross core scheduling frequency drop bisected to 0c313cb20732 "Doug Smythies" <dsmythies@telus.net> - 2016-04-10 09:20 +0200
                Re: [regression] cross core scheduling frequency drop bisected to  0c313cb20732 Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-10 11:40 +0200
                Re: [regression] cross core scheduling frequency drop bisected to  0c313cb20732 Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-10 17:00 +0200
        Re: [regression] cross core scheduling frequency drop bisected to  0c313cb20732 Peter Zijlstra <peterz@infradead.org> - 2016-04-09 13:10 +0200
          Re: [regression] cross core scheduling frequency drop bisected to 0c313cb20732 "Rafael J. Wysocki" <rafael@kernel.org> - 2016-04-09 14:40 +0200
            Re: [regression] cross core scheduling frequency drop bisected to  0c313cb20732 Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-10 17:50 +0200
              Re: [regression] cross core scheduling frequency drop bisected to  0c313cb20732 Rik van Riel <riel@redhat.com> - 2016-04-10 22:30 +0200
                Re: [regression] cross core scheduling frequency drop bisected to  0c313cb20732 Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-11 05:10 +0200
                Re: [regression] cross core scheduling frequency drop bisected to  0c313cb20732 Rik van Riel <riel@redhat.com> - 2016-04-11 14:40 +0200
                Re: [regression] cross core scheduling frequency drop bisected to 0c313cb20732 "Rafael J. Wysocki" <rafael@kernel.org> - 2016-04-11 15:30 +0200
                Re: [regression] cross core scheduling frequency drop bisected to  0c313cb20732 Rik van Riel <riel@redhat.com> - 2016-04-11 15:40 +0200

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