linux-kernel - Re: [PATCH 0/2][RFC] Makes sd->flags sysctl writable

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Date:   Mon, 06 Jul 2020 23:11:32 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Chen Yu <yu.c.chen@...el.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2][RFC] Makes sd->flags sysctl writable


On 06/07/20 21:00, Peter Zijlstra wrote:
> On Tue, Jul 07, 2020 at 03:36:13AM +0800, Chen Yu wrote:
>> It was found that recently the flags of sched domain could
>> not be customized via sysctl, which might make it a little
>> inconenient for performance tuning/debugging.
>
> What specific goals do you have? This is a debug interface.

Also, while the update_top_cache_domain() call on sysctl write may work,
you're back to square one as soon as you go through a hotplug cycle, which
is icky.

That said, I second Peter in that I'm curious as to what you're really
using this interface for. Manually hacking the default / arch topology
flags is a bit tedious, but it's doable.