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From:   Thomas Gleixner <tglx@linutronix.de>
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Matt Fleming <matt@codeblueprint.co.uk>
Subject: Re: [PATCH] signal: Allow RT tasks to cache one sigqueue struct
In-Reply-To: <m11rcu7nbr.fsf@fess.ebiederm.org>
References: <20210303142025.wbbt2nnr6dtgwjfi@linutronix.de> <m1zgzj7uv2.fsf@fess.ebiederm.org> <20210304081142.digtkddajkadwwq5@linutronix.de> <87tupr55ea.fsf@nanos.tec.linutronix.de> <m11rcu7nbr.fsf@fess.ebiederm.org>
Date:   Thu, 04 Mar 2021 21:58:17 +0100
Message-ID: <87lfb263h2.fsf@nanos.tec.linutronix.de>
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On Thu, Mar 04 2021 at 13:04, Eric W. Biederman wrote:
> Thomas Gleixner <tglx@linutronix.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