[PATCH] drm/nouveau: wait for the exclusive fence after the shared ones v2

[Christian König]

Am 11.12.21 um 10:59 schrieb Stefan Fritsch:
> On 09.12.21 11:23, Christian König wrote:
>> Always waiting for the exclusive fence resulted on some performance
>> regressions. So try to wait for the shared fences first, then the
>> exclusive fence should always be signaled already.
>>
>> v2: fix incorrectly placed "(", add some comment why we do this.
>>
>> Signed-off-by: Christian König <christian.koenig at amd.com>
>
> Tested-by: Stefan Fritsch <sf at sfritsch.de>

Thanks.

>
> Please also add a cc for linux-stable, so that this is fixed in 5.15.x

Sure, but I still need some acked-by or rb from one of the Nouveau guys. 
So gentle ping on that.

Regards,
Christian.

>
> Cheers,
> Stefan
>
>> ---
>>   drivers/gpu/drm/nouveau/nouveau_fence.c | 28 +++++++++++++------------
>>   1 file changed, 15 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.c 
>> b/drivers/gpu/drm/nouveau/nouveau_fence.c
>> index 05d0b3eb3690..0ae416aa76dc 100644
>> --- a/drivers/gpu/drm/nouveau/nouveau_fence.c
>> +++ b/drivers/gpu/drm/nouveau/nouveau_fence.c
>> @@ -353,15 +353,22 @@ nouveau_fence_sync(struct nouveau_bo *nvbo, 
>> struct nouveau_channel *chan, bool e
>>             if (ret)
>>               return ret;
>> -    }
>>   -    fobj = dma_resv_shared_list(resv);
>> -    fence = dma_resv_excl_fence(resv);
>> +        fobj = NULL;
>> +    } else {
>> +        fobj = dma_resv_shared_list(resv);
>> +    }
>>   -    if (fence) {
>> +    /* Waiting for the exclusive fence first causes performance 
>> regressions
>> +     * under some circumstances. So manually wait for the shared 
>> ones first.
>> +     */
>> +    for (i = 0; i < (fobj ? fobj->shared_count : 0) && !ret; ++i) {
>>           struct nouveau_channel *prev = NULL;
>>           bool must_wait = true;
>>   +        fence = rcu_dereference_protected(fobj->shared[i],
>> +                        dma_resv_held(resv));
>> +
>>           f = nouveau_local_fence(fence, chan->drm);
>>           if (f) {
>>               rcu_read_lock();
>> @@ -373,20 +380,13 @@ nouveau_fence_sync(struct nouveau_bo *nvbo, 
>> struct nouveau_channel *chan, bool e
>>             if (must_wait)
>>               ret = dma_fence_wait(fence, intr);
>> -
>> -        return ret;
>>       }
>>   -    if (!exclusive || !fobj)
>> -        return ret;
>> -
>> -    for (i = 0; i < fobj->shared_count && !ret; ++i) {
>> +    fence = dma_resv_excl_fence(resv);
>> +    if (fence) {
>>           struct nouveau_channel *prev = NULL;
>>           bool must_wait = true;
>>   -        fence = rcu_dereference_protected(fobj->shared[i],
>> -                        dma_resv_held(resv));
>> -
>>           f = nouveau_local_fence(fence, chan->drm);
>>           if (f) {
>>               rcu_read_lock();
>> @@ -398,6 +398,8 @@ nouveau_fence_sync(struct nouveau_bo *nvbo, 
>> struct nouveau_channel *chan, bool e
>>             if (must_wait)
>>               ret = dma_fence_wait(fence, intr);
>> +
>> +        return ret;
>>       }
>>         return ret;