linux-kernel - Re: [PATCH] smp: Evaluate local cond

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Message-ID: <cc8e8ed4-0181-492a-aff4-71ce5841c891@intel.com>
Date: Tue, 3 Dec 2024 17:38:30 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Rik van Riel <riel@...riel.com>
Cc: linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
 Ingo Molnar <mingo@...nel.org>,
 Linus Torvalds <torvalds@...ux-foundation.org>, Mel Gorman
 <mgorman@...e.de>, x86@...nel.org
Subject: Re: [PATCH] smp: Evaluate local cond_func() before IPI side-effects

On 12/3/24 10:39, Mathieu Desnoyers wrote:
> If cond_func() depends on loading shared state updated by other CPU's
> IPI handlers func(), then triggering execution of remote CPUs IPI before
> evaluating cond_func() may have unexpected consequences.

I always thought this was on purpose so cond_func() can be executed in
parallel with the remote work.

Could we double-check that this doesn't meaningfully slow down IPIs that
have longer work to do?