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Date:   Mon, 24 Jan 2022 09:06:39 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Yury Norov <yury.norov@gmail.com>
Cc:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Andrew Morton <akpm@linux-foundation.org>,
        =?utf-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= <mirq-linux@rere.qmqm.pl>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        David Laight <David.Laight@aculab.com>,
        Joe Perches <joe@perches.com>, Dennis Zhou <dennis@kernel.org>,
        Emil Renner Berthing <kernel@esmil.dk>,
        Nicholas Piggin <npiggin@gmail.com>,
        Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>,
        Alexey Klimov <aklimov@redhat.com>,
        linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 48/54] kernel/time: replace cpumask_weight with
 cpumask_weight_eq where appropriate
Message-ID: <20220124080639.GK20638@worktop.programming.kicks-ass.net>
References: <20220123183925.1052919-1-yury.norov@gmail.com>
 <20220123183925.1052919-49-yury.norov@gmail.com>
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On Sun, Jan 23, 2022 at 10:39:19AM -0800, Yury Norov wrote:
> tick_cleanup_dead_cpu() calls cpumask_weight() to compare the weight
> of cpumask with a given number. We can do it more efficiently with
> cpumask_weight_eq() because conditional cpumask_weight may stop
> traversing the cpumask earlier, as soon as condition is met.

But again, nobody gives a crap about performance here..

> Signed-off-by: Yury Norov <yury.norov@gmail.com>
> ---
>  kernel/time/clockevents.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
> index 003ccf338d20..32d6629a55b2 100644
> --- a/kernel/time/clockevents.c
> +++ b/kernel/time/clockevents.c
> @@ -648,7 +648,7 @@ void tick_cleanup_dead_cpu(int cpu)
>  	 */
>  	list_for_each_entry_safe(dev, tmp, &clockevent_devices, list) {
>  		if (cpumask_test_cpu(cpu, dev->cpumask) &&
> -		    cpumask_weight(dev->cpumask) == 1 &&
> +		    cpumask_weight_eq(dev->cpumask, 1) &&
>  		    !tick_is_broadcast_device(dev)) {
>  			BUG_ON(!clockevent_state_detached(dev));
>  			list_del(&dev->list);
> -- 
> 2.30.2
>