Re: wake_wide mechanism clarification

From	Mike Galbraith <umgwanakikbuti@gmail.com>
Newsgroups	linux.kernel
Subject	Re: wake_wide mechanism clarification
Date	2017-07-31 15:50 +0200
Message-ID	<u9jf4-6U3-19@gated-at.bofh.it> (permalink)
References	(6 earlier) <u8Bxp-40f-13@gated-at.bofh.it> <u8Gno-7k6-7@gated-at.bofh.it> <u8Ipc-a9-5@gated-at.bofh.it> <u8IIy-h0-9@gated-at.bofh.it> <u9hZE-6eS-11@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

On Mon, 2017-07-31 at 12:21 +0000, Josef Bacik wrote:
> 
> I've been working in this area recently because of a cpu imbalance problem.
> Wake_wide() definitely makes it so we're waking affine way too often, but I
> think messing with wake_waide to solve that problem is the wrong solution.  This
> is just a heuristic to see if we should wake affine, the simpler the better.  I
> solved the problem of waking affine too often like this
> 
> https://marc.info/?l=linux-kernel&m=150003849602535&w=2

Wait a minute, that's not quite fair :)  Wake_wide() can't be blamed
for causing too frequent affine wakeups when what it does is filter
some out.  While it may not reject aggressively enough for you (why you
bent it up to be very aggressive), seems the problem from your loads
POV is the scheduler generally being too eager to bounce.

I've also played with rate limiting migration per task, but it had
negative effects too: when idle/periodic balance pulls buddies apart,
rate limiting inhibits them quickly finding each other again, making
undoing all that hard load balancer work a throughput win.  Sigh.

	-Mike

Thread

Re: wake_wide mechanism clarification Joel Fernandes <joelaf@google.com> - 2017-07-29 10:10 +0200
  Re: wake_wide mechanism clarification Joel Fernandes <joelaf@google.com> - 2017-07-29 10:20 +0200
    Re: wake_wide mechanism clarification Michael Wang <yun.wang@profitbricks.com> - 2017-08-02 10:30 +0200
      Re: wake_wide mechanism clarification Joel Fernandes <joelaf@google.com> - 2017-08-04 01:50 +0200
  Re: wake_wide mechanism clarification Mike Galbraith <umgwanakikbuti@gmail.com> - 2017-07-29 17:10 +0200
    Re: wake_wide mechanism clarification Joel Fernandes <joelaf@google.com> - 2017-07-29 22:20 +0200
      Re: wake_wide mechanism clarification Joel Fernandes <joelaf@google.com> - 2017-07-30 00:30 +0200
        Re: wake_wide mechanism clarification Joel Fernandes <joelaf@google.com> - 2017-07-30 00:50 +0200
          Re: wake_wide mechanism clarification Josef Bacik <josef@toxicpanda.com> - 2017-07-31 14:30 +0200
            Re: wake_wide mechanism clarification Mike Galbraith <umgwanakikbuti@gmail.com> - 2017-07-31 15:50 +0200
              Re: wake_wide mechanism clarification Josef Bacik <josef@toxicpanda.com> - 2017-07-31 16:50 +0200
                Re: wake_wide mechanism clarification Mike Galbraith <umgwanakikbuti@gmail.com> - 2017-07-31 19:30 +0200
            Re: wake_wide mechanism clarification Joel Fernandes <joelaf@google.com> - 2017-07-31 18:30 +0200
              Re: wake_wide mechanism clarification Josef Bacik <josef@toxicpanda.com> - 2017-07-31 18:50 +0200
                Re: wake_wide mechanism clarification Joel Fernandes <joelaf@google.com> - 2017-07-31 20:00 +0200

csiph-web