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

[Christian König]

Am 21.12.21 um 11:11 schrieb Thorsten Leemhuis:
> Hi, this is your Linux kernel regression tracker speaking.
>
> CCing Dave and Daniel.
>
> On 15.12.21 23:32, Ben Skeggs wrote:
>> On Tue, 14 Dec 2021 at 19:19, Christian König
>> <ckoenig.leichtzumerken at gmail.com> wrote:
>>> 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.
>> Acked-by: Ben Skeggs <bskeggs at redhat.com>
> What's the status of this patch? I checked a few git trees, but either
> it's not there or it missed it.

You missed it. I've pushed it to drm-misc-fixes about 2 hours ago: 
https://cgit.freedesktop.org/drm/drm-misc/log/?h=drm-misc-fixes

Regards,
Christian.

>
> Reminder, it's a regression already introduced in v5.15, hence all users
> of the current stable kernel are affected by it, so it would be nice to
> get the fix on its way now that Ben acked it and Dan tested it.
>
> Ciao, Thorsten
>
> P.S.: As a Linux kernel regression tracker I'm getting a lot of reports
> on my table. I can only look briefly into most of them. Unfortunately
> therefore I sometimes will get things wrong or miss something important.
> I hope that's not the case here; if you think it is, don't hesitate to
> tell me about it in a public reply. That's in everyone's interest, as
> what I wrote above might be misleading to everyone reading this; any
> suggestion I gave thus might sent someone reading this down the wrong
> rabbit hole, which none of us wants.
>
> BTW, I have no personal interest in this issue, which is tracked using
> regzbot, my Linux kernel regression tracking bot
> (https://linux-regtracking.leemhuis.info/regzbot/). I'm only posting
> this mail to get things rolling again and hence don't need to be CC on
> all further activities wrt to this regression.
>
> #regzbot poke
>
>>>>> ---
>>>>>    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;