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From: Thomas Gleixner <tglx@linutronix.de>
To: Yury Norov <yury.norov@gmail.com>, linux-kernel@vger.kernel.org, Greg
 Kroah-Hartman <gregkh@linuxfoundation.org>, "Paul E. McKenney"
 <paulmck@kernel.org>, "Rafael J. Wysocki" <rafael@kernel.org>, Anna-Maria
 Behnsen <anna-maria@linutronix.de>, Ben Segall <bsegall@google.com>, Daniel
 Bristot de Oliveira <bristot@redhat.com>, Dietmar Eggemann
 <dietmar.eggemann@arm.com>, Frederic Weisbecker <frederic@kernel.org>,
 Imran Khan <imran.f.khan@oracle.com>, Ingo Molnar <mingo@redhat.com>,
 Johannes Weiner <hannes@cmpxchg.org>, Juri Lelli <juri.lelli@redhat.com>,
 Leonardo Bras <leobras@redhat.com>, Mel Gorman <mgorman@suse.de>, Peter
 Zijlstra <peterz@infradead.org>, Rik van Riel <riel@surriel.com>, Steven
 Rostedt <rostedt@goodmis.org>, Tejun Heo <tj@kernel.org>, Valentin
 Schneider <vschneid@redhat.com>, Vincent Guittot
 <vincent.guittot@linaro.org>, Waiman Long <longman@redhat.com>, Yury Norov
 <yury.norov@gmail.com>, Zefan Li <lizefan.x@bytedance.com>,
 cgroups@vger.kernel.org
Subject: Re: [PATCH 6/6] tick/common: optimize cpumask_equal() usage
In-Reply-To: <878r0cn6a5.ffs@tglx>
References: <20240513220146.1461457-1-yury.norov@gmail.com>
 <20240513220146.1461457-7-yury.norov@gmail.com> <878r0cn6a5.ffs@tglx>
Date: Tue, 14 May 2024 10:42:46 +0200
Message-ID: <874jb0n5rt.ffs@tglx>
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On Tue, May 14 2024 at 10:31, Thomas Gleixner wrote:
> On Mon, May 13 2024 at 15:01, Yury Norov wrote:
>> Some functions in the file call cpumask_equal() with src1p == src2p.
>> We can obviously just skip comparison entirely in this case.
>>
>> This patch fixes cpumask_equal invocations when boot-test or LTP detect
>> such condition.
>
> Please write your changelogs in imperative mood.
>
> git grep 'This patch' Documentation/process/
>
> Also please see Documentation/process/maintainer-tip.rst
>
>> Signed-off-by: Yury Norov <yury.norov@gmail.com>
>> ---
>>  kernel/time/tick-common.c | 15 +++++++++++----
>>  1 file changed, 11 insertions(+), 4 deletions(-)
>>
>> diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
>> index d88b13076b79..b31fef292833 100644
>> --- a/kernel/time/tick-common.c
>> +++ b/kernel/time/tick-common.c
>> @@ -253,7 +253,8 @@ static void tick_setup_device(struct tick_device *td,
>>  	 * When the device is not per cpu, pin the interrupt to the
>>  	 * current cpu:
>>  	 */
>> -	if (!cpumask_equal(newdev->cpumask, cpumask))
>> +	if (newdev->cpumask != cpumask &&
>> +			!cpumask_equal(newdev->cpumask, cpumask))
>>  		irq_set_affinity(newdev->irq, cpumask);
>
> I'm not seeing the benefit. This is slow path setup code so the extra
> comparison does not really buy anything aside of malformatted line
> breaks.

Instead of sprinkling these conditional all over the place, can't you
just do the obvious and check for ptr1 == ptr2 in bitmap_copy() and
bitmap_equal()?

Thanks,

	tglx