linux-kernel - Re: [PATCH 09/34] dmaengine: idxd: optimize perfmon_assign

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Message-ID: <0bfc5c56-467e-40ef-b0ee-0a15d7f64e33@intel.com>
Date:   Mon, 20 Nov 2023 08:34:41 -0700
From:   Dave Jiang <dave.jiang@...el.com>
To:     Yury Norov <yury.norov@...il.com>, <linux-kernel@...r.kernel.org>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Vinod Koul <vkoul@...nel.org>, <dmaengine@...r.kernel.org>
CC:     Jan Kara <jack@...e.cz>,
        Mirsad Todorovac <mirsad.todorovac@....unizg.hr>,
        Matthew Wilcox <willy@...radead.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Maxim Kuvyrkov <maxim.kuvyrkov@...aro.org>,
        Alexey Klimov <klimov.linux@...il.com>,
        "Fenghua Yu" <fenghua.yu@...el.com>,
        "tom.zanussi@...ux.intel.com" <tom.zanussi@...ux.intel.com>
Subject: Re: [PATCH 09/34] dmaengine: idxd: optimize perfmon_assign_event()



On 11/18/23 08:50, Yury Norov wrote:
> The function searches used_mask for a set bit in a for-loop bit by bit.
> We can do it faster by using atomic find_and_set_bit().
> 
> Signed-off-by: Yury Norov <yury.norov@...il.com>

Reviewed-by: Dave Jiang <dave.jiang@...el.com>
> ---
>  drivers/dma/idxd/perfmon.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/dma/idxd/perfmon.c b/drivers/dma/idxd/perfmon.c
> index fdda6d604262..4dd9c0d979c3 100644
> --- a/drivers/dma/idxd/perfmon.c
> +++ b/drivers/dma/idxd/perfmon.c
> @@ -134,13 +134,9 @@ static void perfmon_assign_hw_event(struct idxd_pmu *idxd_pmu,
>  static int perfmon_assign_event(struct idxd_pmu *idxd_pmu,
>  				struct perf_event *event)
>  {
> -	int i;
> -
> -	for (i = 0; i < IDXD_PMU_EVENT_MAX; i++)
> -		if (!test_and_set_bit(i, idxd_pmu->used_mask))
> -			return i;
> +	int i = find_and_set_bit(idxd_pmu->used_mask, IDXD_PMU_EVENT_MAX);
>  
> -	return -EINVAL;
> +	return i < IDXD_PMU_EVENT_MAX ? i : -EINVAL;
>  }
>  
>  /*