linux-kernel - Re: [PATCH 09/16] irq: don't copy cpu affinity mask if source is equal to destination

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Date:   Mon, 18 Jul 2022 23:30:31 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yury Norov <yury.norov@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Alexey Klimov <aklimov@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Ben Segall <bsegall@...gle.com>,
        Christoph Lameter <cl@...ux.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dennis Zhou <dennis@...nel.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Eric Dumazet <edumazet@...gle.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Ingo Molnar <mingo@...hat.com>,
        Isabella Basso <isabbasso@...eup.net>,
        John Fastabend <john.fastabend@...il.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Juergen Gross <jgross@...e.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        KP Singh <kpsingh@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Martin KaFai Lau <kafai@...com>,
        Mel Gorman <mgorman@...e.de>, Miroslav Benes <mbenes@...e.cz>,
        Nathan Chancellor <nathan@...nel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Song Liu <songliubraving@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tejun Heo <tj@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Valentin Schneider <vschneid@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Vlastimil Babka <vbabka@...e.cz>, Yonghong Song <yhs@...com>,
        linux-mm@...ck.org, netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH 09/16] irq: don't copy cpu affinity mask if source is
 equal to destination

On Mon, Jul 18, 2022 at 12:28:37PM -0700, Yury Norov wrote:

>  kernel/irq/manage.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
> index 8c396319d5ac..f9c1b21584ec 100644
> --- a/kernel/irq/manage.c
> +++ b/kernel/irq/manage.c
> @@ -284,7 +284,8 @@ int irq_do_set_affinity(struct irq_data *data, const struct cpumask *mask,
>  	switch (ret) {
>  	case IRQ_SET_MASK_OK:
>  	case IRQ_SET_MASK_OK_DONE:
> -		cpumask_copy(desc->irq_common_data.affinity, mask);
> +		if (desc->irq_common_data.affinity != mask)
> +			cpumask_copy(desc->irq_common_data.affinity, mask);

Seems like mostly pointless logic at this point. This is not a
performance senstive operation afaik.

>  		fallthrough;
>  	case IRQ_SET_MASK_OK_NOCOPY:
>  		irq_validate_effective_affinity(data);
> -- 
> 2.34.1
>