On 8/17/2021 4:36 PM, Michel Dänzer wrote:
On 2021-08-17 12:37 p.m., Lazar, Lijo wrote:
On 8/17/2021 3:29 PM, Michel Dänzer wrote:
On 2021-08-17 11:37 a.m., Lazar, Lijo wrote:
On 8/17/2021 2:56 PM, Michel Dänzer wrote:
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@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 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@xxxxxxxxxxxxxxx
Reviewed-by: Lijo Lazar <lijo.lazar@xxxxxxx> # v3
Acked-by: Christian König <christian.koenig@xxxxxxx> # v3
Signed-off-by: Michel Dänzer <mdaenzer@xxxxxxxxxx>
---
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.
To clarify - when nothing is scheduled. If enable() is called when the count is 0, it goes to unlock. Now the expectation is someone to call Disable first.
Yes, the very first amdgpu_gfx_off_ctrl call must pass enable=false, or it's a bug, which
if (WARN_ON_ONCE(adev->gfx.gfx_off_req_count == 0))
will catch.
Let's say Disable() is called first, then the variable will be false, right?
Ohh, I see what you mean. The first time amdgpu_gfx_off_ctrl is called with enable=false, adev->gfx.gfx_off_state == false (what it was initialized to), so it doesn't actually disable GFXOFF in HW.
Exactly.
Turns out that's not the end of that rabbit (side-)hole yet. :)
amdgpu_device_init initializes adev->gfx.gfx_off_req_count = 1. amdgpu_gfx_off_ctrl is then called with enable=true from amdgpu_device_init → amdgpu_device_ip_late_init → amdgpu_device_set_pg_state. This schedules amdgpu_device_delay_enable_gfx_off, which runs ~100ms later, enables GFXOFF in the HW and sets adev->gfx.gfx_off_state = true.
What if a disable comes at < 100ms? Quite unlikely, neverthless in that
case pending work will get cancelled and the variable won't be set until
the work gets a chance to fully run. The assumption that GFXOFF disable
succeeded in a subsequent amdgpu_gfx_off_ctrl enable = false won't be
correct as PMFW will by default enable GFXOFF when there is no activity.
Otherwise, keep an assumption that amdgpu_device_delay_enable_gfx_off
gets a chance to run before any disable call comes - maybe that's the
case in most cases.
So it looks fine as is actually, if a bit convoluted.
(I wonder if GFXOFF shouldn't rather be enabled synchronously during initialization though)
Yes, that is logical. But amdgpu_device_ip_late_init is called also
during amdgpu_device_resume. amdgpu_device_resume is used in pm_ops or
runtime pm. In those cases it makes sense to delay it as there could be
an immediate usage of GFX.
Thanks,
Lijo
