[PATCH RFC 0/6] amdgpu: Avoid powering on the dGPU on vkEnumeratePhysicalDevices()

[Christian König]

On 06.08.25 12:15, Philipp Zabel wrote:
> On Mi, 2025-08-06 at 10:58 +0200, Christian König wrote:
>> On 31.07.25 07:36, Philipp Zabel wrote:
>>> This is an attempt at fixing amd#2295 [1]:
>>>
>>>   On an AMD Rembrandt laptop with 680M iGPU and 6700S dGPU, calling
>>>   vkEnumeratePhysicalDevices() wakes up the sleeping dGPU, even if all
>>>   the application wants is to find and use the iGPU. This causes a delay
>>>   of about 2 seconds on this system, followed by a few seconds of
>>>   increased power draw until runtime PM turns the dGPU back off again.
>>>
>>> [1] https://gitlab.freedesktop.org/drm/amd/-/issues/2295
>>>
>>> Patch 1 avoids power up on some ioctls that don't need it.
>>> Patch 2 avoids power up on open() by postponing fpriv initialization to
>>> the first ioctl() that wakes up the dGPU.
>>> Patches 3 and 4 add AMDGPU_INFO to the list of non-waking ioctls,
>>> returning cached values for some queries.
>>> Patch 5 works around an explicit register access from libdrm.
>>> Patch 6 shorts out the syncobj ioctls while fpriv is still
>>> uninitialized. This avoids waking up the dGPU during Vulkan syncobj
>>> feature detection.
>>
>> This idea came up multiple times now but was never completed.
>>
>> IIRC Pierre-Eric last worked on it, it would probably be a good idea to dig up his patches from the mailing list.
> 
> Thank you, I wasn't aware of those patches [1]. Pierre-Eric did mention
> them in https://gitlab.freedesktop.org/mesa/mesa/-/issues/13001, but I
> didn't pick up on that back then.
> 
> [1] https://lore.kernel.org/all/20240618153003.146168-1-pierre-eric.pelloux-prayer@amd.com/
> 
> Is that the latest version?

I honestly don't know. @Pierre-Eric?

> It looks to me like the review stalled out
> on a disagreement whether the GB_ADDR_CONFIG query should be a separate
> ioctl or whether it should be added to drm_amdgpu_info_device. The
> discussion was later continued at
> https://gitlab.freedesktop.org/mesa/libdrm/-/merge_requests/368,
> seemingly coming to the conclusion that keeping the register read (but
> cached) is the way to go? I didn't find a newer series with that
> implemented.

Could be that Pierre-Eric dropped the work after that.

But IIRC we already use a cached value for GB_ADDR_CONFIG because of GFXOFF.

Regards,
Christian.

> 
>>>
>>> regards
>>> Philipp
>>>
>>> Signed-off-by: Philipp Zabel <p.zabel at pengutronix.de>
>>> ---
>>> Alex Deucher (1):
>>>       drm/amdgpu: don't wake up the GPU for some IOCTLs
>>>
>>> Philipp Zabel (5):
>>>       drm/amdgpu: don't wake up the GPU when opening the device
>>>       drm/amdgpu: don't query xclk in AMDGPU_INFO_DEV_INFO
>>>       drm/amdgpu: don't wake up the GPU for some AMDGPU_INFO queries
>>>       drm/amdgpu: don't wake up the GPU for mmGB_ADDR_CONFIG register read
>>
>> That is both unnecessary an insufficient. Unnecessary because we already have a mechanism to cache register values and insufficient because IIRC you need to add a bunch of more registers to the cached list.
> 
> This series was (just barely) sufficient for my purpose, which was only
> to make vkEnumeratePhysicalDevices() not wake the dGPU on my Laptop.
> I didn't realize there already was a caching mechanism in the lower
> layers.
> 
>> See Pierre-Erics latest patch set, I think we already solved that but I'm not 100% sure.
> 
> If I found the correct version, it seems Sima's suggestion of pushing
> runtime pm handling down from amdgpu_drm_ioctl into the amdgpu ioctl
> callbacks [2] would be the best first next step?
> 
> [2] https://lore.kernel.org/amd-gfx/ZnvJHwnNAvDrRMVG@phenom.ffwll.local/
> 
> regards
> Philipp