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Re: sched: tweak select_idle_sibling to look for idle threads

From Peter Zijlstra <peterz@infradead.org>
Newsgroups linux.kernel
Subject Re: sched: tweak select_idle_sibling to look for idle threads
Date 2016-05-03 20:30 +0200
Message-ID <ruNf3-4Gi-1@gated-at.bofh.it> (permalink)
References (4 earlier) <ruhIe-dd-5@gated-at.bofh.it> <runuj-5gi-33@gated-at.bofh.it> <runDZ-5IL-19@gated-at.bofh.it> <ruoA1-6AD-13@gated-at.bofh.it> <ruGQi-7ml-23@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On Tue, May 03, 2016 at 01:31:31PM +0200, Peter Zijlstra wrote:
> Then flip on the last_idle tracking in select_idle_core():
> 
> root@ivb-ep:~/bench/sysbench# for i in NO_OLD_IDLE NO_ORDER_IDLE IDLE_CORE NO_FORCE_CORE IDLE IDLE_SMT IDLE_LAST NO_IDLE_FIRST ; do echo $i > /debug/sched_features ; done ; ./doit-psql 30 2 5 10 20 40 80
>   2: [30 secs]     transactions:                        54355  (1811.78 per sec.)
>   5: [30 secs]     transactions:                        122609 (4086.81 per sec.)
>  10: [30 secs]     transactions:                        238738 (7957.66 per sec.)
>  20: [30 secs]     transactions:                        354693 (11822.49 per sec.)
>  40: [30 secs]     transactions:                        421807 (14059.32 per sec.)
>  80: [30 secs]     transactions:                        427088 (14234.25 per sec.)
> 
> 
> And see the top end collapse..

> +	if (sched_feat(IDLE_CORE)) {
> +		if (test_idle_cores(target)) {
> +			i = select_idle_core(p, start);
> +			if ((unsigned)i < nr_cpumask_bits)
> +				return i;
>  
>  			/*
> +			 * Failed to find an idle core; stop looking for one.
>  			 */
> +			clear_idle_cores(target);
> +		}
>  	}

'Obvious' bug there; if we start returning idle threads; we'll not get
to clear_idle_cores() and the thing remains active and badness happens.

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Thread

Re: sched: tweak select_idle_sibling to look for idle threads Peter Zijlstra <peterz@infradead.org> - 2016-04-30 14:50 +0200
  Re: sched: tweak select_idle_sibling to look for idle threads Mike Galbraith <mgalbraith@suse.de> - 2016-05-01 09:20 +0200
    Re: sched: tweak select_idle_sibling to look for idle threads Peter Zijlstra <peterz@infradead.org> - 2016-05-01 11:00 +0200
      Re: sched: tweak select_idle_sibling to look for idle threads Mike Galbraith <mgalbraith@suse.de> - 2016-05-01 11:30 +0200
        Re: sched: tweak select_idle_sibling to look for idle threads Yuyang Du <yuyang.du@intel.com> - 2016-05-07 11:10 +0200
          Re: sched: tweak select_idle_sibling to look for idle threads Mike Galbraith <mgalbraith@suse.de> - 2016-05-08 10:10 +0200
            Re: sched: tweak select_idle_sibling to look for idle threads Yuyang Du <yuyang.du@intel.com> - 2016-05-09 04:40 +0200
              Re: sched: tweak select_idle_sibling to look for idle threads Mike Galbraith <mgalbraith@suse.de> - 2016-05-09 05:50 +0200
                Re: sched: tweak select_idle_sibling to look for idle threads Yuyang Du <yuyang.du@intel.com> - 2016-05-09 06:10 +0200
                Re: sched: tweak select_idle_sibling to look for idle threads Mike Galbraith <mgalbraith@suse.de> - 2016-05-09 09:50 +0200
                Re: sched: tweak select_idle_sibling to look for idle threads Yuyang Du <yuyang.du@intel.com> - 2016-05-09 11:00 +0200
                Re: sched: tweak select_idle_sibling to look for idle threads Mike Galbraith <mgalbraith@suse.de> - 2016-05-09 11:40 +0200
                Re: sched: tweak select_idle_sibling to look for idle threads Yuyang Du <yuyang.du@intel.com> - 2016-05-10 09:10 +0200
                Re: sched: tweak select_idle_sibling to look for idle threads Mike Galbraith <mgalbraith@suse.de> - 2016-05-10 09:50 +0200
                Re: sched: tweak select_idle_sibling to look for idle threads Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-05-10 17:30 +0200
                Re: sched: tweak select_idle_sibling to look for idle threads Yuyang Du <yuyang.du@intel.com> - 2016-05-11 05:00 +0200
                Re: sched: tweak select_idle_sibling to look for idle threads Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-05-11 06:20 +0200
                Re: sched: tweak select_idle_sibling to look for idle threads Yuyang Du <yuyang.du@intel.com> - 2016-05-11 11:10 +0200
                Re: sched: tweak select_idle_sibling to look for idle threads Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-05-11 12:00 +0200
              Re: sched: tweak select_idle_sibling to look for idle threads Mike Galbraith <mgalbraith@suse.de> - 2016-05-09 06:00 +0200
                Re: sched: tweak select_idle_sibling to look for idle threads Yuyang Du <yuyang.du@intel.com> - 2016-05-09 06:20 +0200
    Re: sched: tweak select_idle_sibling to look for idle threads Peter Zijlstra <peterz@infradead.org> - 2016-05-02 10:50 +0200
      Re: sched: tweak select_idle_sibling to look for idle threads Mike Galbraith <mgalbraith@suse.de> - 2016-05-02 17:00 +0200
        Re: sched: tweak select_idle_sibling to look for idle threads Peter Zijlstra <peterz@infradead.org> - 2016-05-02 17:00 +0200
          Re: sched: tweak select_idle_sibling to look for idle threads Chris Mason <clm@fb.com> - 2016-05-02 17:50 +0200
            Re: sched: tweak select_idle_sibling to look for idle threads Peter Zijlstra <peterz@infradead.org> - 2016-05-03 16:40 +0200
              Re: sched: tweak select_idle_sibling to look for idle threads Chris Mason <clm@fb.com> - 2016-05-03 17:20 +0200
                Re: sched: tweak select_idle_sibling to look for idle threads Peter Zijlstra <peterz@infradead.org> - 2016-05-04 12:40 +0200
                Re: sched: tweak select_idle_sibling to look for idle threads Peter Zijlstra <peterz@infradead.org> - 2016-05-04 17:40 +0200
                Re: sched: tweak select_idle_sibling to look for idle threads Matt Fleming <matt@codeblueprint.co.uk> - 2016-05-06 00:10 +0200
                Re: sched: tweak select_idle_sibling to look for idle threads Mike Galbraith <mgalbraith@suse.de> - 2016-05-06 21:00 +0200
                Re: sched: tweak select_idle_sibling to look for idle threads Peter Zijlstra <peterz@infradead.org> - 2016-05-09 10:40 +0200
                Re: sched: tweak select_idle_sibling to look for idle threads Mike Galbraith <mgalbraith@suse.de> - 2016-05-09 11:00 +0200
                Re: sched: tweak select_idle_sibling to look for idle threads Peter Zijlstra <peterz@infradead.org> - 2016-05-04 17:50 +0200
                Re: sched: tweak select_idle_sibling to look for idle threads Chris Mason <clm@fb.com> - 2016-05-04 19:50 +0200
                Re: sched: tweak select_idle_sibling to look for idle threads Peter Zijlstra <peterz@infradead.org> - 2016-05-05 11:40 +0200
                Re: sched: tweak select_idle_sibling to look for idle threads Chris Mason <clm@fb.com> - 2016-05-05 16:00 +0200
                Re: sched: tweak select_idle_sibling to look for idle threads Peter Zijlstra <peterz@infradead.org> - 2016-05-06 09:20 +0200
                Re: sched: tweak select_idle_sibling to look for idle threads Chris Mason <clm@fb.com> - 2016-05-06 19:30 +0200
                Re: sched: tweak select_idle_sibling to look for idle threads Peter Zijlstra <peterz@infradead.org> - 2016-05-06 09:30 +0200
          Re: sched: tweak select_idle_sibling to look for idle threads Mike Galbraith <mgalbraith@suse.de> - 2016-05-02 19:40 +0200
        Re: sched: tweak select_idle_sibling to look for idle threads Peter Zijlstra <peterz@infradead.org> - 2016-05-02 17:10 +0200
          Re: sched: tweak select_idle_sibling to look for idle threads Ingo Molnar <mingo@kernel.org> - 2016-05-02 18:10 +0200
            Re: sched: tweak select_idle_sibling to look for idle threads Peter Zijlstra <peterz@infradead.org> - 2016-05-03 13:40 +0200
              Re: sched: tweak select_idle_sibling to look for idle threads Peter Zijlstra <peterz@infradead.org> - 2016-05-03 20:30 +0200
        Re: sched: tweak select_idle_sibling to look for idle threads Peter Zijlstra <peterz@infradead.org> - 2016-05-02 17:20 +0200

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