linux-kernel - Re: [RFC][PATCH 00/16] sched: Core scheduling

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Date:   Tue, 12 Mar 2019 12:07:31 -0700
From:   Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Aubrey Li <aubrey.intel@...il.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paul Turner <pjt@...gle.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Fr?d?ric Weisbecker <fweisbec@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Greg Kerr <kerrnel@...gle.com>,
        Subhra Mazumdar <subhra.mazumdar@...cle.com>
Subject: Re: [RFC][PATCH 00/16] sched: Core scheduling

Hi,

With core scheduling LTP reports 2 new failures related to cgroups(memcg_stat_rss and memcg_move_charge_at_immigrate). I will try to debug it.

Also "perf sched map" indicates there might be a small window when 2 processes in different cgroups run together on one core.
In below case B0 and D0(stress-ng-cpu and sysbench) belong to 2 different cgroups with cpu.tag enabled.

$ perf sched map

  *A0                                 382.266600 secs A0 => kworker/0:1-eve:51
  *B0                                 382.266612 secs B0 => stress-ng-cpu:7956
  *A0                                 382.394597 secs 
  *B0                                 382.394609 secs 
   B0             *C0                 382.494459 secs C0 => i915/signal:0:450
   B0             *D0                 382.494468 secs D0 => sysbench:8088
  *.               D0                 382.494472 secs .  => swapper:0
   .              *C0                 383.095787 secs 
  *B0              C0                 383.095792 secs 
   B0             *D0                 383.095820 secs
  *A0              D0                 383.096587 secs

In some cases I dont see an IPI getting sent to sibling cpu when 2 incompatible processes are picked. Like is below logs at timestamp 382.146250
"stress-ng-cpu" is picked when "sysbench" is running on the sibling cpu.

  kworker/0:1-51    [000] d...   382.146246: __schedule: cpu(0): selected: stress-ng-cpu/7956 ffff9945bad29200
  kworker/0:1-51    [000] d...   382.146246: __schedule: max: stress-ng-cpu/7956 ffff9945bad29200
  kworker/0:1-51    [000] d...   382.146247: __prio_less: (swapper/4/0;140,0,0) ?< (sysbench/8088;140,34783671987,0)
  kworker/0:1-51    [000] d...   382.146248: __prio_less: (stress-ng-cpu/7956;119,34817170203,0) ?< (sysbench/8088;119,34783671987,0)
  kworker/0:1-51    [000] d...   382.146249: __schedule: cpu(4): selected: sysbench/8088 ffff9945a7405200
  kworker/0:1-51    [000] d...   382.146249: __prio_less: (stress-ng-cpu/7956;119,34817170203,0) ?< (sysbench/8088;119,34783671987,0)
  kworker/0:1-51    [000] d...   382.146250: __schedule: picked: stress-ng-cpu/7956 ffff9945bad29200
  kworker/0:1-51    [000] d...   382.146251: __switch_to: Pawan: cpu(0) switching to stress-ng-cpu
  kworker/0:1-51    [000] d...   382.146251: __switch_to: Pawan: cpu(4) running sysbench
stress-ng-cpu-7956  [000] dN..   382.274234: __schedule: cpu(0): selected: kworker/0:1/51 0
stress-ng-cpu-7956  [000] dN..   382.274235: __schedule: max: kworker/0:1/51 0
stress-ng-cpu-7956  [000] dN..   382.274235: __schedule: cpu(4): selected: sysbench/8088 ffff9945a7405200
stress-ng-cpu-7956  [000] dN..   382.274237: __prio_less: (kworker/0:1/51;119,50744489595,0) ?< (sysbench/8088;119,34911643157,0)
stress-ng-cpu-7956  [000] dN..   382.274237: __schedule: picked: kworker/0:1/51 0
stress-ng-cpu-7956  [000] d...   382.274239: __switch_to: Pawan: cpu(0) switching to kworker/0:1
stress-ng-cpu-7956  [000] d...   382.274239: __switch_to: Pawan: cpu(4) running sysbench

-Pawan