linux-kernel - Re: [PATCH v4] posix-timers: Prefer delivery of signals to the current thread

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Message-ID: <20230128195641.GA14906@redhat.com>
Date:   Sat, 28 Jan 2023 20:56:42 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Marco Elver <elver@...gle.com>, linux-kernel@...r.kernel.org,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Frederic Weisbecker <frederic@...nel.org>
Subject: Re: [PATCH v4] posix-timers: Prefer delivery of signals to the
 current thread

Dmitry,

I agree with what you said, just one note...

On 01/27, Dmitry Vyukov wrote:
>
> After this change the test passes quickly (within a second for me).

yet perhaps it makes sense to slightly change it? It does

	+static void *distribution_thr(void *arg) {
	+	while (__atomic_load_n(&remain, __ATOMIC_RELAXED));
	+	return NULL;
	+}

so distribution_thr() eats CPU even after this thread gets a signal and thus
(in theory) it can "steal" cpu_timer_fire() from other threads unpredictably
long ? How about

	-	while (__atomic_load_n(&remain, __ATOMIC_RELAXED));
	+	while (__atomic_load_n(&got_signal, __ATOMIC_RELAXED));

?

Oleg.