linux-kernel - Re: [GIT PULL] Bitmap patches for v5.19-rc1

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Date:   Sat, 4 Jun 2022 14:24:52 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Yury Norov <yury.norov@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [GIT PULL] Bitmap patches for v5.19-rc1

On Fri, Jun 3, 2022 at 12:48 PM Yury Norov <yury.norov@...il.com> wrote:
>
>       arch/ia64: replace cpumask_weight with cpumask_empty where appropriate

As you can tell from the pr-tracker-bot reply, I've pulled this.

But I did want to point out that this patch should probably have gone further.

That first argument to per_cpu_scan_finalize() is kind of ugly, but it
should probably have been something like

    n = cpumask_weight(&early_cpu_possible_map) ? : 32;

instead of doing *both* cpumask_weight() and cpumask_empty().

The only case cpumask_empty() can be optimized if it's not entirely
empty, but that's the also the case where that code then ends up
calling cpumask_weight() to get the final result.

Note: I don't really care. This is ia64 boot-time setup code, so it's
not like performance matters. It's dead and irrelevant. I just reacted
to "that patch tries to micro-optimize the code, but is missing the
forest for the trees".

                     Linus