linux-kernel - Re: [PATCH] cpu: memoise number of possible cpus

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Message-Id: <20240418132600.ffbf4d53b39eaaeaffc28198@linux-foundation.org>
Date: Thu, 18 Apr 2024 13:26:00 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Alexey Dobriyan <adobriyan@...il.com>
Cc: tglx@...utronix.de, peterz@...radead.org, yury.norov@...il.com,
 linux@...musvillemoes.dk, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpu: memoise number of possible cpus

On Thu, 18 Apr 2024 07:19:27 +0300 Alexey Dobriyan <adobriyan@...il.com> wrote:

> cpu_possible_mask is fixed after boot, so it makes sense
> to calculate number of possible cpus to
> a) make num_possible_cpus() faster (distros ship with _large_ NR_CPUS),
> b) unscrew codegen elsewhere replacing function call
>    with simple memory load.

There are a lot of calls to set_cpu_possible().  Perhaps calculating
num_possible_cpus within there would reduce risk of things getting out
of sync, either now or in the future.

reset_cpu_possible_mask() appears to have no callers.  Kill?