linux-kernel - Re: [PATCH v12 2/3] sched: Move task_mm_cid_work to mm work

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Message-ID: <20250409140303.GA9833@noisy.programming.kicks-ass.net>
Date: Wed, 9 Apr 2025 16:03:03 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Gabriele Monaco <gmonaco@...hat.com>
Cc: linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	"Paul E. McKenney" <paulmck@...nel.org>, linux-mm@...ck.org,
	Ingo Molnar <mingo@...hat.org>, Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH v12 2/3] sched: Move task_mm_cid_work to mm work_struct

On Tue, Mar 11, 2025 at 07:28:45AM +0100, Gabriele Monaco wrote:
> +static inline void rseq_preempt_from_tick(struct task_struct *t)
> +{
> +	u64 rtime = t->se.sum_exec_runtime - t->se.prev_sum_exec_runtime;
> +
> +	if (rtime > RSEQ_UNPREEMPTED_THRESHOLD)
> +		rseq_preempt(t);
> +}

This confused me.

The goal seems to be to tickle __rseq_handle_notify_resume() so it'll
end up queueing that work thing. But why do we want to set PREEMPT_BIT
here?