linux-kernel - Re: [PATCH 08/16] smp: optimize smp_call_function_many

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Message-ID: <YtXQom+a5C+iXSvm@worktop.programming.kicks-ass.net>
Date:   Mon, 18 Jul 2022 23:29:06 +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>,
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        Tejun Heo <tj@...nel.org>,
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        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 08/16] smp: optimize smp_call_function_many_cond() for
 more

On Mon, Jul 18, 2022 at 12:28:36PM -0700, Yury Norov wrote:

> ---
>  kernel/smp.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/smp.c b/kernel/smp.c
> index 7ed2b9b12f74..f96fdf944b4a 100644
> --- a/kernel/smp.c
> +++ b/kernel/smp.c
> @@ -942,7 +942,11 @@ static void smp_call_function_many_cond(const struct cpumask *mask,
>  
>  	if (run_remote) {
>  		cfd = this_cpu_ptr(&cfd_data);
> -		cpumask_and(cfd->cpumask, mask, cpu_online_mask);
> +		if (mask == cpu_online_mask)
> +			cpumask_copy(cfd->cpumask, cpu_online_mask);
> +		else
> +			cpumask_and(cfd->cpumask, mask, cpu_online_mask);
> +

Or... you could optimize cpumask_and() to detect the src1p == src2p case?

>  		__cpumask_clear_cpu(this_cpu, cfd->cpumask);
>  
>  		cpumask_clear(cfd->cpumask_ipi);
> -- 
> 2.34.1
>