linux-kernel - Re: [PATCH 2/2] drm/amdkfd: Slighly optimize 'init_doorbell

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Date:   Mon, 22 Nov 2021 16:44:20 -0500
From:   Felix Kuehling <felix.kuehling@....com>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        alexander.deucher@....com, christian.koenig@....com,
        Xinhui.Pan@....com, airlied@...ux.ie, daniel@...ll.ch
Cc:     amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 2/2] drm/amdkfd: Slighly optimize 'init_doorbell_bitmap()'

Am 2021-11-21 um 12:41 p.m. schrieb Christophe JAILLET:
> The 'doorbell_bitmap' bitmap has just been allocated. So we can use the
> non-atomic '__set_bit()' function to save a few cycles as no concurrent
> access can happen.
>
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>

Thank you for the patches. I think the same sort of change (at least the
allocation/freeing part) could be applied to the queue_slot_bitmap in
kfd_process_queue_manager.c. Would you like to submit another revision
of this patch series that handles that as well?

Either way, this series is

Reviewed-by: Felix Kuehling <Felix.Kuehling@....com>


> ---
> bitmap_set() could certainly also be use, but range checking would be
> tricky.
> ---
>  drivers/gpu/drm/amd/amdkfd/kfd_process.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_process.c b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
> index 172ee8763523..2e9d341062c4 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_process.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
> @@ -1447,9 +1447,9 @@ static int init_doorbell_bitmap(struct qcm_process_device *qpd,
>  
>  	for (i = 0; i < KFD_MAX_NUM_OF_QUEUES_PER_PROCESS / 2; i++) {
>  		if (i >= range_start && i <= range_end) {
> -			set_bit(i, qpd->doorbell_bitmap);
> -			set_bit(i + KFD_QUEUE_DOORBELL_MIRROR_OFFSET,
> -				qpd->doorbell_bitmap);
> +			__set_bit(i, qpd->doorbell_bitmap);
> +			__set_bit(i + KFD_QUEUE_DOORBELL_MIRROR_OFFSET,
> +				  qpd->doorbell_bitmap);
>  		}
>  	}
>