Re: [PATCH 33/49] perf: replace bitmap_weight with bitmap_weight_eq for ThunderX2

From: Mark Rutland <mark.rutland@arm.com>
To: Yury Norov <yury.norov@gmail.com>, Will Deacon <will@kernel.org>
Cc: "Andy Shevchenko" <andriy.shevchenko@linux.intel.com>,
	"Rasmus Villemoes" <linux@rasmusvillemoes.dk>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Michał Mirosław" <mirq-linux@rere.qmqm.pl>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Peter Zijlstra" <peterz@infradead.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,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 33/49] perf: replace bitmap_weight with bitmap_weight_eq for ThunderX2
Date: Fri, 11 Feb 2022 10:30:37 +0000	[thread overview]
Message-ID: <YgY6zb7FT/lifZfd@FVFF77S0Q05N> (raw)
In-Reply-To: <20220210224933.379149-34-yury.norov@gmail.com>

On Thu, Feb 10, 2022 at 02:49:17PM -0800, Yury Norov wrote:
> tx2_uncore_event_start() calls bitmap_weight() to compare the weight
> of bitmap with a given number. We can do it more efficiently with
> bitmap_weight_eq because conditional bitmap_weight may stop traversing
> the bitmap earlier, as soon as condition is (or can't be) met.
> 
> Signed-off-by: Yury Norov <yury.norov@gmail.com>

Given the max counters value is either 4 or 8 I doubt this should matter, but
for consistenct this is fine, so:

Acked-by: Mark Rutland <mark.rutland@arm.com>

I now see bitmap_weight_eq() is introduced within this series, so I assume you
need to queue that and its users together, and will want to take the prior
drivers/perf/ bit together with that.

Thanks,
Mark.

> ---
>  drivers/perf/thunderx2_pmu.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/perf/thunderx2_pmu.c b/drivers/perf/thunderx2_pmu.c
> index 1edb9c03704f..97d5b39778fa 100644
> --- a/drivers/perf/thunderx2_pmu.c
> +++ b/drivers/perf/thunderx2_pmu.c
> @@ -623,8 +623,8 @@ static void tx2_uncore_event_start(struct perf_event *event, int flags)
>  		return;
>  
>  	/* Start timer for first event */
> -	if (bitmap_weight(tx2_pmu->active_counters,
> -				tx2_pmu->max_counters) == 1) {
> +	if (bitmap_weight_eq(tx2_pmu->active_counters,
> +				tx2_pmu->max_counters, 1)) {
>  		hrtimer_start(&tx2_pmu->hrtimer,
>  			ns_to_ktime(tx2_pmu->hrtimer_interval),
>  			HRTIMER_MODE_REL_PINNED);
> -- 
> 2.32.0
> 

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