[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <87jzjwkszb.ffs@tglx>
Date: Tue, 14 May 2024 23:02:00 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Yury Norov <yury.norov@...il.com>, linux-kernel@...r.kernel.org, Greg
Kroah-Hartman <gregkh@...uxfoundation.org>, "Paul E. McKenney"
<paulmck@...nel.org>, "Rafael J. Wysocki" <rafael@...nel.org>, Anna-Maria
Behnsen <anna-maria@...utronix.de>, Ben Segall <bsegall@...gle.com>,
Daniel Bristot de Oliveira <bristot@...hat.com>, Dietmar Eggemann
<dietmar.eggemann@....com>, Frederic Weisbecker <frederic@...nel.org>,
Imran Khan <imran.f.khan@...cle.com>, Ingo Molnar <mingo@...hat.com>,
Johannes Weiner <hannes@...xchg.org>, Juri Lelli <juri.lelli@...hat.com>,
Leonardo Bras <leobras@...hat.com>, Mel Gorman <mgorman@...e.de>, Peter
Zijlstra <peterz@...radead.org>, Rik van Riel <riel@...riel.com>, Steven
Rostedt <rostedt@...dmis.org>, Tejun Heo <tj@...nel.org>, Valentin
Schneider <vschneid@...hat.com>, Vincent Guittot
<vincent.guittot@...aro.org>, Waiman Long <longman@...hat.com>, Yury Norov
<yury.norov@...il.com>, Zefan Li <lizefan.x@...edance.com>,
cgroups@...r.kernel.org
Subject: Re: [PATCH 3/6] driver core: cpu: optimize print_cpus_isolated()
On Mon, May 13 2024 at 15:01, Yury Norov wrote:
> The function may be called with housekeeping_cpumask == cpu_possible_mask,
How so? There is no cpumask argument in the function signature. Can you
please be precise?
> and in such case the 'isolated' cpumask would be just empty.
>
> We can call cpumask_clear() in that case, and save CPU cycles.
>
> @@ -282,8 +282,10 @@ static ssize_t print_cpus_isolated(struct device *dev,
> if (!alloc_cpumask_var(&isolated, GFP_KERNEL))
> return -ENOMEM;
>
> - cpumask_andnot(isolated, cpu_possible_mask,
> - housekeeping_cpumask(HK_TYPE_DOMAIN));
> + if (cpu_possible_mask != housekeeping_cpumask(HK_TYPE_DOMAIN))
> + cpumask_andnot(isolated, cpu_possible_mask, housekeeping_cpumask(HK_TYPE_DOMAIN));
> + else
> + cpumask_clear(isolated);
> len = sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(isolated));
>
> free_cpumask_var(isolated);
Seriously? You need clear() to emit an empty string via %*pbl?
if (cpu_possible_mask != housekeeping_cpumask(HK_TYPE_DOMAIN)) {
if (!alloc_cpumask_var(&isolated, GFP_KERNEL))
return -ENOMEM;
cpumask_andnot(isolated, cpu_possible_mask, housekeeping_cpumask(HK_TYPE_DOMAIN));
len = sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(isolated));
free_cpumask_var(isolated);
} else {
len = sysfs_emit(buf, "\n");
}
That actually would make sense and spare way more CPU cycles, no?
Is it actually worth the larger text size? Not really convinced about that.
Thanks,
tglx
Powered by blists - more mailing lists