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

[Alex Deucher]

Applied.  Let's see how long this one lasts :)

Alex

On Tue, Aug 17, 2021 at 4:23 AM Michel Dänzer <michel at daenzer.net> 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 &&
> +                           !amdgpu_dpm_set_powergating_by_smu(adev, AMD_IP_BLOCK_TYPE_GFX, false)) {
> +                               adev->gfx.gfx_off_state = false;
>
> -                       if (adev->gfx.funcs->init_spm_golden) {
> -                               dev_dbg(adev->dev, "GFXOFF is disabled, re-init SPM golden settings\n");
> -                               amdgpu_gfx_init_spm_golden(adev);
> +                               if (adev->gfx.funcs->init_spm_golden) {
> +                                       dev_dbg(adev->dev,
> +                                               "GFXOFF is disabled, re-init SPM golden settings\n");
> +                                       amdgpu_gfx_init_spm_golden(adev);
> +                               }
>                         }
>                 }
> +
> +               adev->gfx.gfx_off_req_count++;
>         }
>
> +unlock:
>         mutex_unlock(&adev->gfx.gfx_off_mutex);
>  }
>
> --
> 2.32.0
>