linux-kernel - Re: [PATCH 12/49] perf: replace bitmap_weight with bitmap

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Date:   Fri, 11 Feb 2022 18:27:56 +0100
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Yury Norov <yury.norov@...il.com>,
        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>,
        Peter Zijlstra <peterz@...radead.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, Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Shaokun Zhang <zhangshaokun@...ilicon.com>,
        Qi Liu <liuqi115@...wei.com>,
        Khuong Dinh <khuong@...amperecomputing.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 12/49] perf: replace bitmap_weight with bitmap_empty where
 appropriate

Le 10/02/2022 à 23:48, Yury Norov a écrit :
> In some places, drivers/perf code calls bitmap_weight() to check if any
> bit of a given bitmap is set. It's better to use bitmap_empty() in that
> case because bitmap_empty() stops traversing the bitmap as soon as it
> finds first set bit, while bitmap_weight() counts all bits unconditionally.
> 
> Signed-off-by: Yury Norov <yury.norov@...il.com>
> ---
>   drivers/perf/arm-cci.c                   | 2 +-
>   drivers/perf/arm_pmu.c                   | 4 ++--
>   drivers/perf/hisilicon/hisi_uncore_pmu.c | 2 +-
>   drivers/perf/xgene_pmu.c                 | 2 +-
>   4 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/perf/arm-cci.c b/drivers/perf/arm-cci.c
> index 54aca3a62814..96e09fa40909 100644
> --- a/drivers/perf/arm-cci.c
> +++ b/drivers/perf/arm-cci.c
> @@ -1096,7 +1096,7 @@ static void cci_pmu_enable(struct pmu *pmu)
>   {
>   	struct cci_pmu *cci_pmu = to_cci_pmu(pmu);
>   	struct cci_pmu_hw_events *hw_events = &cci_pmu->hw_events;
> -	int enabled = bitmap_weight(hw_events->used_mask, cci_pmu->num_cntrs);
> +	bool enabled = !bitmap_empty(hw_events->used_mask, cci_pmu->num_cntrs);
>   	unsigned long flags;
>   
>   	if (!enabled)
> diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
> index 295cc7952d0e..a31b302b0ade 100644
> --- a/drivers/perf/arm_pmu.c
> +++ b/drivers/perf/arm_pmu.c
> @@ -524,7 +524,7 @@ static void armpmu_enable(struct pmu *pmu)
>   {
>   	struct arm_pmu *armpmu = to_arm_pmu(pmu);
>   	struct pmu_hw_events *hw_events = this_cpu_ptr(armpmu->hw_events);
> -	int enabled = bitmap_weight(hw_events->used_mask, armpmu->num_events);
> +	bool enabled = !bitmap_empty(hw_events->used_mask, armpmu->num_events);
>   
>   	/* For task-bound events we may be called on other CPUs */
>   	if (!cpumask_test_cpu(smp_processor_id(), &armpmu->supported_cpus))
> @@ -785,7 +785,7 @@ static int cpu_pm_pmu_notify(struct notifier_block *b, unsigned long cmd,
>   {
>   	struct arm_pmu *armpmu = container_of(b, struct arm_pmu, cpu_pm_nb);
>   	struct pmu_hw_events *hw_events = this_cpu_ptr(armpmu->hw_events);
> -	int enabled = bitmap_weight(hw_events->used_mask, armpmu->num_events);
> +	bool enabled = !bitmap_empty(hw_events->used_mask, armpmu->num_events);
>   
>   	if (!cpumask_test_cpu(smp_processor_id(), &armpmu->supported_cpus))
>   		return NOTIFY_DONE;
> diff --git a/drivers/perf/hisilicon/hisi_uncore_pmu.c b/drivers/perf/hisilicon/hisi_uncore_pmu.c
> index a738aeab5c04..358e4e284a62 100644
> --- a/drivers/perf/hisilicon/hisi_uncore_pmu.c
> +++ b/drivers/perf/hisilicon/hisi_uncore_pmu.c
> @@ -393,7 +393,7 @@ EXPORT_SYMBOL_GPL(hisi_uncore_pmu_read);
>   void hisi_uncore_pmu_enable(struct pmu *pmu)
>   {
>   	struct hisi_pmu *hisi_pmu = to_hisi_pmu(pmu);
> -	int enabled = bitmap_weight(hisi_pmu->pmu_events.used_mask,
> +	bool enabled = !bitmap_empty(hisi_pmu->pmu_events.used_mask,
>   				    hisi_pmu->num_counters);
>   
>   	if (!enabled)
> diff --git a/drivers/perf/xgene_pmu.c b/drivers/perf/xgene_pmu.c
> index 5283608dc055..0c32dffc7ede 100644
> --- a/drivers/perf/xgene_pmu.c
> +++ b/drivers/perf/xgene_pmu.c
> @@ -867,7 +867,7 @@ static void xgene_perf_pmu_enable(struct pmu *pmu)
>   {
>   	struct xgene_pmu_dev *pmu_dev = to_pmu_dev(pmu);
>   	struct xgene_pmu *xgene_pmu = pmu_dev->parent;
> -	int enabled = bitmap_weight(pmu_dev->cntr_assign_mask,
> +	bool enabled = !bitmap_empty(pmu_dev->cntr_assign_mask,
>   			pmu_dev->max_counters);

Would it make sense to call it 'disabled', remove the "!"...

>   
>   	if (!enabled)
... and 'if (disabled)' here?

Just my 2c,

CJ