[AMD Official Use Only]
Hi Michel,
The patch seems reasonable to me(especially the cancel_delayed_work_sync() part).
However, can you explain more about the code below?
What's the race issue here exactly?
+ /* mutex_lock could deadlock with cancel_delayed_work_sync in amdgpu_gfx_off_ctrl. */
+ if (!mutex_trylock(&adev->gfx.gfx_off_mutex)) {
+ /* If there's a bug which causes amdgpu_gfx_off_ctrl to be called with enable=true
+ * when adev->gfx.gfx_off_req_count is already 0, we might race with that.
+ * Re-schedule to make sure gfx off will be re-enabled in the HW eventually.
+ */
+ schedule_delayed_work(&adev->gfx.gfx_off_delay_work, AMDGPU_GFX_OFF_DELAY_ENABLE);
+ return;
+ }
BR
Evan
> -----Original Message-----
> From: amd-gfx <amd-gfx-bounces@xxxxxxxxxxxxxxxxxxxxx> On Behalf Of
> Michel Dänzer
> Sent: Friday, August 13, 2021 6:29 PM
> To: Deucher, Alexander <Alexander.Deucher@xxxxxxx>; Koenig, Christian
> <Christian.Koenig@xxxxxxx>
> Cc: Liu, Leo <Leo.Liu@xxxxxxx>; Zhu, James <James.Zhu@xxxxxxx>; amd-
> gfx@xxxxxxxxxxxxxxxxxxxxx; dri-devel@xxxxxxxxxxxxxxxxxxxxx
> Subject: [PATCH] drm/amdgpu: Cancel delayed work when GFXOFF is
> disabled
>
> From: Michel Dänzer <mdaenzer@xxxxxxxxxx>
>
> 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 GFXOFF transitions from
> enabled to disabled. This makes sure the delayed work will be scheduled
> as intended in the reverse case.
>
> In order to avoid a deadlock, amdgpu_device_delay_enable_gfx_off needs
> to use mutex_trylock instead of mutex_lock.
>
> v2:
> * Use cancel_delayed_work_sync & mutex_trylock instead of
> mod_delayed_work.
>
> Signed-off-by: Michel Dänzer <mdaenzer@xxxxxxxxxx>
> ---
> drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 11 ++++++++++-
> drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c | 13 +++++++------
> drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.h | 3 +++
> 3 files changed, 20 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
> b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
> index f3fd5ec710b6..8b025f70706c 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
> @@ -2777,7 +2777,16 @@ 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);
> + /* mutex_lock could deadlock with cancel_delayed_work_sync in
> amdgpu_gfx_off_ctrl. */
> + if (!mutex_trylock(&adev->gfx.gfx_off_mutex)) {
> + /* If there's a bug which causes amdgpu_gfx_off_ctrl to be
> called with enable=true
> + * when adev->gfx.gfx_off_req_count is already 0, we might
> race with that.
> + * Re-schedule to make sure gfx off will be re-enabled in the
> HW eventually.
> + */
> + schedule_delayed_work(&adev->gfx.gfx_off_delay_work,
> AMDGPU_GFX_OFF_DELAY_ENABLE);
> + return;
> + }
> +
> 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;
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c
> b/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c
> index a0be0772c8b3..da4c46db3093 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c
> @@ -28,9 +28,6 @@
> #include "amdgpu_rlc.h"
> #include "amdgpu_ras.h"
>
> -/* delay 0.1 second to enable gfx off feature */
> -#define GFX_OFF_DELAY_ENABLE msecs_to_jiffies(100)
> -
> /*
> * GPU GFX IP block helpers function.
> */
> @@ -569,9 +566,13 @@ void amdgpu_gfx_off_ctrl(struct amdgpu_device
> *adev, bool enable)
> 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)) {
> + schedule_delayed_work(&adev->gfx.gfx_off_delay_work,
> AMDGPU_GFX_OFF_DELAY_ENABLE);
> + } else if (!enable) {
> + if (adev->gfx.gfx_off_req_count == 1 && !adev-
> >gfx.gfx_off_state)
> + 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) {
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.h
> b/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.h
> index d43fe2ed8116..dcdb505bb7f4 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.h
> @@ -32,6 +32,9 @@
> #include "amdgpu_rlc.h"
> #include "soc15.h"
>
> +/* delay 0.1 second to enable gfx off feature */
> +#define AMDGPU_GFX_OFF_DELAY_ENABLE msecs_to_jiffies(100)
> +
> /* GFX current status */
> #define AMDGPU_GFX_NORMAL_MODE 0x00000000L
> #define AMDGPU_GFX_SAFE_MODE 0x00000001L
> --
> 2.32.0
