linux-kernel - Re: [PATCH v6 1/2] posix-timers: Prefer delivery of signals to the current thread

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Message-ID: <CANpmjNNZMHHjbN_5a3Krk1xPvT_WLKGUxueaKjUYJZkeDZ=AKw@mail.gmail.com>
Date:   Thu, 30 Mar 2023 12:19:40 +0200
From:   Marco Elver <elver@...gle.com>
To:     elver@...gle.com, Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>
Cc:     Oleg Nesterov <oleg@...hat.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com
Subject: Re: [PATCH v6 1/2] posix-timers: Prefer delivery of signals to the
 current thread

On Thu, 16 Mar 2023 at 13:31, Marco Elver <elver@...gle.com> wrote:
>
> From: Dmitry Vyukov <dvyukov@...gle.com>
>
> POSIX timers using the CLOCK_PROCESS_CPUTIME_ID clock prefer the main
> thread of a thread group for signal delivery.     However, this has a
> significant downside: it requires waking up a potentially idle thread.
>
> Instead, prefer to deliver signals to the current thread (in the same
> thread group) if SIGEV_THREAD_ID is not set by the user. This does not
> change guaranteed semantics, since POSIX process CPU time timers have
> never guaranteed that signal delivery is to a specific thread (without
> SIGEV_THREAD_ID set).
>
> The effect is that we no longer wake up potentially idle threads, and
> the kernel is no longer biased towards delivering the timer signal to
> any particular thread (which better distributes the timer signals esp.
> when multiple timers fire concurrently).
>
> Signed-off-by: Dmitry Vyukov <dvyukov@...gle.com>
> Suggested-by: Oleg Nesterov <oleg@...hat.com>
> Reviewed-by: Oleg Nesterov <oleg@...hat.com>
> Signed-off-by: Marco Elver <elver@...gle.com>

Gentle ping...

Thanks,
-- Marco