[PATCH] drm/amdgpu: Cancel delayed work when GFXOFF is disabled

[Michel Dänzer]

On 2021-08-17 11:12 a.m., Lazar, Lijo wrote:
> 
> 
> On 8/17/2021 1:53 PM, Michel Dänzer wrote:
>> From: Michel Dänzer <mdaenzer at redhat.com>
>>
>> schedule_delayed_work does not push back the work if it was already
>> scheduled before, so amdgpu_device_delay_enable_gfx_off ran ~100 ms
>> after the first time GFXOFF was disabled and re-enabled, even if GFXOFF
>> was disabled and re-enabled again during those 100 ms.
>>
>> This resulted in frame drops / stutter with the upcoming mutter 41
>> release on Navi 14, due to constantly enabling GFXOFF in the HW and
>> disabling it again (for getting the GPU clock counter).
>>
>> To fix this, call cancel_delayed_work_sync when the disable count
>> transitions from 0 to 1, and only schedule the delayed work on the
>> reverse transition, not if the disable count was already 0. This makes
>> sure the delayed work doesn't run at unexpected times, and allows it to
>> be lock-free.
>>
>> v2:
>> * Use cancel_delayed_work_sync & mutex_trylock instead of
>>    mod_delayed_work.
>> v3:
>> * Make amdgpu_device_delay_enable_gfx_off lock-free (Christian König)
>> v4:
>> * Fix race condition between amdgpu_gfx_off_ctrl incrementing
>>    adev->gfx.gfx_off_req_count and amdgpu_device_delay_enable_gfx_off
>>    checking for it to be 0 (Evan Quan)
>>
>> Cc: stable at vger.kernel.org
>> Reviewed-by: Lijo Lazar <lijo.lazar at amd.com> # v3
>> Acked-by: Christian König <christian.koenig at amd.com> # v3
>> Signed-off-by: Michel Dänzer <mdaenzer at redhat.com>
>> ---
>>
>> Alex, probably best to wait a bit longer before picking this up. :)
>>
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 11 +++----
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c    | 36 +++++++++++++++-------
>>   2 files changed, 30 insertions(+), 17 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>> index f3fd5ec710b6..f944ed858f3e 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>> @@ -2777,12 +2777,11 @@ static void amdgpu_device_delay_enable_gfx_off(struct work_struct *work)
>>       struct amdgpu_device *adev =
>>           container_of(work, struct amdgpu_device, gfx.gfx_off_delay_work.work);
>>   -    mutex_lock(&adev->gfx.gfx_off_mutex);
>> -    if (!adev->gfx.gfx_off_state && !adev->gfx.gfx_off_req_count) {
>> -        if (!amdgpu_dpm_set_powergating_by_smu(adev, AMD_IP_BLOCK_TYPE_GFX, true))
>> -            adev->gfx.gfx_off_state = true;
>> -    }
>> -    mutex_unlock(&adev->gfx.gfx_off_mutex);
>> +    WARN_ON_ONCE(adev->gfx.gfx_off_state);
>> +    WARN_ON_ONCE(adev->gfx.gfx_off_req_count);
>> +
>> +    if (!amdgpu_dpm_set_powergating_by_smu(adev, AMD_IP_BLOCK_TYPE_GFX, true))
>> +        adev->gfx.gfx_off_state = true;
>>   }
>>     /**
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c
>> index a0be0772c8b3..b4ced45301be 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c
>> @@ -563,24 +563,38 @@ void amdgpu_gfx_off_ctrl(struct amdgpu_device *adev, bool enable)
>>         mutex_lock(&adev->gfx.gfx_off_mutex);
>>   -    if (!enable)
>> -        adev->gfx.gfx_off_req_count++;
>> -    else if (adev->gfx.gfx_off_req_count > 0)
>> +    if (enable) {
>> +        /* If the count is already 0, it means there's an imbalance bug somewhere.
>> +         * Note that the bug may be in a different caller than the one which triggers the
>> +         * WARN_ON_ONCE.
>> +         */
>> +        if (WARN_ON_ONCE(adev->gfx.gfx_off_req_count == 0))
>> +            goto unlock;
>> +
>>           adev->gfx.gfx_off_req_count--;
>>   -    if (enable && !adev->gfx.gfx_off_state && !adev->gfx.gfx_off_req_count) {
>> -        schedule_delayed_work(&adev->gfx.gfx_off_delay_work, GFX_OFF_DELAY_ENABLE);
>> -    } else if (!enable && adev->gfx.gfx_off_state) {
>> -        if (!amdgpu_dpm_set_powergating_by_smu(adev, AMD_IP_BLOCK_TYPE_GFX, false)) {
>> -            adev->gfx.gfx_off_state = false;
>> +        if (adev->gfx.gfx_off_req_count == 0 && !adev->gfx.gfx_off_state)
>> +            schedule_delayed_work(&adev->gfx.gfx_off_delay_work, GFX_OFF_DELAY_ENABLE);
>> +    } else {
>> +        if (adev->gfx.gfx_off_req_count == 0) {
>> +            cancel_delayed_work_sync(&adev->gfx.gfx_off_delay_work);
>> +
>> +            if (adev->gfx.gfx_off_state &&
> 
> More of a question which I didn't check last time - Is this expected to be true when the disable call comes in first?

My assumption is that cancel_delayed_work_sync guarantees amdgpu_device_delay_enable_gfx_off's assignment is visible here.


-- 
Earthling Michel Dänzer               |               https://redhat.com
Libre software enthusiast             |             Mesa and X developer