linux-kernel - Re: [RFC PATCH v4] sched: Fix performance regression introduced by mm

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Date:   Wed, 12 Apr 2023 11:10:43 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Aaron Lu <aaron.lu@...el.com>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        linux-kernel@...r.kernel.org, Olivier Dion <odion@...icios.com>,
        michael.christie@...cle.com
Subject: Re: [RFC PATCH v4] sched: Fix performance regression introduced by
 mm_cid

On Tue, Apr 11, 2023 at 09:12:21PM +0800, Aaron Lu wrote:

> Forget about this "v4 is better than v2 and v3" part, my later test
> showed the contention can also rise to around 18% for v4.

So while I can reproduce the initial regression on a HSW-EX system
(4*18*2) and get lovely things like:

  34.47%--schedule_hrtimeout_range_clock
          schedule
          |
          --34.42%--__schedule
                    |
                    |--31.86%--_raw_spin_lock
                    |          |
                    |           --31.65%--native_queued_spin_lock_slowpath
	            |
                    --0.72%--dequeue_task_fair
                             |
                             --0.60%--dequeue_entity

On a --threads=144 run; it is completely gone when I use v4:

  6.92%--__schedule
         |
         |--2.16%--dequeue_task_fair
         |          |
         |           --1.69%--dequeue_entity
         |                     |
         |                     |--0.61%--update_load_avg
         |                     |
         |                      --0.54%--update_curr
         |
         |--1.30%--pick_next_task_fair
         |          |
         |           --0.54%--set_next_entity
         |
         |--0.77%--psi_task_switch
         |
         --0.69%--switch_mm_irqs_off


:-(