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Message-ID: <Ytg2EA+2XtzPiyBE@yury-laptop> Date: Wed, 20 Jul 2022 10:06:24 -0700 From: Yury Norov <yury.norov@...il.com> To: Peter Zijlstra <peterz@...radead.org> 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 08/16] smp: optimize smp_call_function_many_cond() for more On Mon, Jul 18, 2022 at 11:29:06PM +0200, Peter Zijlstra wrote: > 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? This is not what I would consider as optimization. For vast majority of users this check is useless because they know for sure that cpumasks are different. For this case I can invent something like cpumask_and_check_eq(), so that there'll be minimal impact on user code. (Suggestions for a better name are very welcome.) Thanks, Yury
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