linux-kernel - Re: [PATCH] task_work: allow TWA_SIGNAL without a rescheduling IPI

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Message-ID: <20220428090836.GQ2731@worktop.programming.kicks-ass.net>
Date:   Thu, 28 Apr 2022 11:08:36 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     LKML <linux-kernel@...r.kernel.org>, tglx@...utronix.de
Subject: Re: [PATCH] task_work: allow TWA_SIGNAL without a rescheduling IPI

On Mon, Apr 25, 2022 at 07:52:31PM -0600, Jens Axboe wrote:
> On 4/22/22 8:34 AM, Jens Axboe wrote:
> > Some use cases don't always need an IPI when sending a TWA_SIGNAL
> > notification. Add TWA_SIGNAL_NO_IPI, which is just like TWA_SIGNAL,
> > except it doesn't send an IPI to the target task. It merely sets
> > TIF_NOTIFY_SIGNAL and wakes up the task.

Could you perphaps elaborate on those use-cases? How do they guarantee
the task_work is ran before userspace?