linux-kernel - Re: [PATCH v2 1/4] drm/sched: Enable signaling for finished fence

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Message-ID: <ffb5acca-7c20-4497-d7d0-25508a6566d2@amd.com>
Date:   Tue, 6 Sep 2022 15:55:44 -0400
From:   Andrey Grodzovsky <andrey.grodzovsky@....com>
To:     Christian König <christian.koenig@....com>,
        Arvind Yadav <Arvind.Yadav@....com>, shashank.sharma@....com,
        amaranath.somalapuram@....com, Arunpravin.PaneerSelvam@....com,
        sumit.semwal@...aro.org, gustavo@...ovan.org, airlied@...ux.ie,
        daniel@...ll.ch, linux-media@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/4] drm/sched: Enable signaling for finished fence


On 2022-09-06 02:34, Christian König wrote:
> Am 05.09.22 um 18:34 schrieb Arvind Yadav:
>> Here's enabling software signaling for finished fence.
>>
>> Signed-off-by: Arvind Yadav <Arvind.Yadav@....com>
>> ---
>>
>> Changes in v1 :
>> 1- Addressing Christian's comment to remove CONFIG_DEBUG_FS check from
>> this patch.
>> 2- The version of this patch is also changed and previously
>> it was [PATCH 2/4]
>>
>> ---
>>   drivers/gpu/drm/scheduler/sched_main.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/scheduler/sched_main.c 
>> b/drivers/gpu/drm/scheduler/sched_main.c
>> index e0ab14e0fb6b..fe72de0e2911 100644
>> --- a/drivers/gpu/drm/scheduler/sched_main.c
>> +++ b/drivers/gpu/drm/scheduler/sched_main.c
>> @@ -962,6 +962,8 @@ static int drm_sched_main(void *param)
>>               /* Drop for original kref_init of the fence */
>>               dma_fence_put(fence);
>>   + dma_fence_enable_sw_signaling(&s_fence->finished);
>
> Ok, this makes it a lot clearer. Previously I though that we have some 
> bug in dma_fence_add_callback().
>
> This is essentially the wrong place to call this, the finished fence 
> should be enabled by the caller and not here.
>
> There is also another problem in dma_fence_enable_sw_signaling(), it 
> returns early when the fence is already signaled:
>
>         if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
>                 return;
>
> Please remove that one first.


Why we even need this explicit call if dma_fence_add_callback calls 
__dma_fence_enable_signaling anyway ?

Andrey


>
> Thanks,
> Christian.
>
>
>> +
>>               r = dma_fence_add_callback(fence, &sched_job->cb,
>>                              drm_sched_job_done_cb);
>>               if (r == -ENOENT)
>