linux-kernel - Re: [PATCH 22/49] sched: replace cpumask_weight with cpumask

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Date:   Fri, 11 Feb 2022 06:19:41 -0800
From:   Yury Norov <yury.norov@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        David Laight <David.Laight@...lab.com>,
        Joe Perches <joe@...ches.com>, Dennis Zhou <dennis@...nel.org>,
        Emil Renner Berthing <kernel@...il.dk>,
        Nicholas Piggin <npiggin@...il.com>,
        Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
        Alexey Klimov <aklimov@...hat.com>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [PATCH 22/49] sched: replace cpumask_weight with cpumask_empty
 where appropriate

On Fri, Feb 11, 2022 at 11:19:58AM +0100, Peter Zijlstra wrote:
> On Thu, Feb 10, 2022 at 02:49:06PM -0800, Yury Norov wrote:
> > In some places, kernel/sched code calls cpumask_weight() to check if
> > any bit of a given cpumask is set. We can do it more efficiently with
> > cpumask_empty() because cpumask_empty() stops traversing the cpumask as
> > soon as it finds first set bit, while cpumask_weight() counts all bits
> > unconditionally.
> > 
> > Signed-off-by: Yury Norov <yury.norov@...il.com>
> 
> Neither of these paths are really performance sentitive, but whatever.
> 
> Do you want me to take this now,

Yes please. Many patches from this series already merged this way.

> or do you want to merge the whole
> series somewere else? In which case:
> 
> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> 
> > ---
> >  kernel/sched/core.c     | 2 +-
> >  kernel/sched/topology.c | 2 +-
> >  2 files changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 28d1b7af03dc..ed7b392945b7 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -8711,7 +8711,7 @@ int cpuset_cpumask_can_shrink(const struct cpumask *cur,
> >  {
> >  	int ret = 1;
> >  
> > -	if (!cpumask_weight(cur))
> > +	if (cpumask_empty(cur))
> >  		return ret;
> >  
> >  	ret = dl_cpuset_cpumask_can_shrink(cur, trial);
> > diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> > index d201a7052a29..8478e2a8cd65 100644
> > --- a/kernel/sched/topology.c
> > +++ b/kernel/sched/topology.c
> > @@ -74,7 +74,7 @@ static int sched_domain_debug_one(struct sched_domain *sd, int cpu, int level,
> >  			break;
> >  		}
> >  
> > -		if (!cpumask_weight(sched_group_span(group))) {
> > +		if (cpumask_empty(sched_group_span(group))) {
> >  			printk(KERN_CONT "\n");
> >  			printk(KERN_ERR "ERROR: empty group\n");
> >  			break;
> > -- 
> > 2.32.0
> >