linux-kernel - Re: [PATCH] sched_ext: Provide a sysfs enable

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Message-ID: <ZvGJ_xT2LhYJHQbZ@slm.duckdns.org>
Date: Mon, 23 Sep 2024 05:32:15 -1000
From: Tejun Heo <tj@...nel.org>
To: Phil Auld <pauld@...hat.com>
Cc: andrea.righi@...ux.dev, David Vernet <void@...ifault.com>,
	Giovanni Gherdovich <giovanni.gherdovich@...e.com>,
	Kleber Sacilotto de Souza <kleber.souza@...onical.com>,
	Marcelo Henrique Cerri <marcelo.cerri@...onical.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched_ext: Provide a sysfs enable_seq counter

Hello,

On Mon, Sep 23, 2024 at 12:45:48PM +0200, Phil Auld wrote:
...
> It's not a per scheduler counter, though. It's global. We want to know

Yeah, the sequence is global but we can report the sequence at which a given
scheduler is loaded on each scheduler. That way, e.g., you can tell whether
a particular scheduler instance is the same one you looked at the last time
too.

> that a (any) scx scheduler has been loaded at some time in the past. It's
> really only interesting when 0 or > 0. The actual non-zero number and which
> scheduler(s) don't matter that much.

Not necessarily. e.g. You can also detect scheduler failing or being updated
for other reasons.

> And it needs to persist when the scheduler is unloaded (I didn't look but
> I uspect the per scheduler attrs come and go?).

Yes, the load sequence number should stay persistent across all schedulers,
but each scheduler should report the sequence number at which *it* was
loaded. Note that this doesn't really change anything now. If you only care
whether any SCX scheduler has ever been loaded, you'd always look under
root.

Thanks.

-- 
tejun