linux-kernel - Re: [PATCH] signal: Allow RT tasks to cache one sigqueue struct

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Message-ID: <87lfb263h2.fsf@nanos.tec.linutronix.de>
Date:   Thu, 04 Mar 2021 21:58:17 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Matt Fleming <matt@...eblueprint.co.uk>
Subject: Re: [PATCH] signal: Allow RT tasks to cache one sigqueue struct

On Thu, Mar 04 2021 at 13:04, Eric W. Biederman wrote:
> Thomas Gleixner <tglx@...utronix.de> writes:
>>
>> We could of course do the caching unconditionally for all tasks.
>
> Is there any advantage to only doing this for realtime tasks?

It was mostly to avoid tons of cached entries hanging around all over
the place. So I limited it to the case which the RT users deeply cared
about. Also related to the accounting question below.

> If not it probably makes sense to do the caching for all tasks.
>
> I am wondering if we want to count the cached sigqueue structure to the
> users rt signal rlimit?

That makes some sense, but that's a user visible change as a single
signal will up the count for a tasks lifetime while today it is removed
from accounting again once the signal is delivered. So that needs some
thought.

Thanks,

        tglx