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

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Message-ID: <20230412142616.GI628377@hirez.programming.kicks-ass.net>
Date:   Wed, 12 Apr 2023 16:26:16 +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 Wed, Apr 12, 2023 at 07:42:40PM +0800, Aaron Lu wrote:

> I *guess* you might be able to see some contention with hackbench on
> that HSW-EX system with v4.

Indeed! Notably it seems to be the wakeup from idle that trips it
hardest:

11.31%     0.03%  swapper          [kernel.vmlinux]            [k] schedule_idle
        |
        --11.28%--schedule_idle
                  |
                  --11.27%--__schedule
                            |
                            |--8.61%--mm_cid_get
                            |          |
                            |           --5.78%--_raw_spin_lock
                            |                     |
                            |                      --5.56%--native_queued_spin_lock_slowpath
                            |
                            |--0.81%--finish_task_switch.isra.0
                            |          |
                            |           --0.69%--asm_sysvec_call_function_single
                            |                     |
                            |                      --0.58%--sysvec_call_function_single
                            |
                            --0.57%--switch_mm_irqs_off