Re: [PATCH 3/3] drm/amdgpu: skip kfd resume_process for dev_pm_ops.thaw()

["Lazar, Lijo" <lijo.lazar@amd.com>]

On 7/2/2025 7:24 PM, Alex Deucher wrote:
> On Wed, Jul 2, 2025 at 3:24 AM Sam <guoqzhan@amd.com> wrote:
>>
>>
>> On 2025/7/2 00:07, Alex Deucher wrote:
>>> On Tue, Jul 1, 2025 at 4:32 AM Christian König <christian.koenig@amd.com> wrote:
>>>> On 01.07.25 10:03, Zhang, GuoQing (Sam) wrote:
>>>>> thaw() is called before writing the hiberation image to swap disk. See
>>>>> the doc here.
>>>>> https://github.com/torvalds/linux/blob/v6.14/Documentation/driver-api/pm/devices.rst?plain=1#L552 <https://github.com/torvalds/linux/blob/v6.14/Documentation/driver-api/pm/devices.rst?plain=1#L552>
>>>>>
>>>>> And amdgpu implemented thaw() callback by calling amdgpu_device_resume().
>>>>> https://github.com/torvalds/linux/blob/v6.14/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c#L2572 <https://github.com/torvalds/linux/blob/v6.14/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c#L2572>
>>>>>
>>>>> This patch is skip amdgpu_amdkfd_resume_process() call in thaw() during
>>>>> hibernation. it is not skipped in restore() during resume from
>>>>> hibernation when system boot again.
>>>>>
>>>>>
>>>>> I just found the following kernel doc. Thaw() is intended to resume the
>>>>> storage device for saving the hibernation image.
>>>> Ah, that makes much more sense.
>>>>
>>>>> Our GPU is not involved
>>>>> in it, it is not necessary to resume our GPU in thaw().
>>>>> https://github.com/torvalds/linux/blob/v6.14/Documentation/power/pci.rst?plain=1#L588 <https://github.com/torvalds/linux/blob/v6.14/Documentation/power/pci.rst?plain=1#L588>
>>>>>
>>>>> So another implementation is to remove the amdgpu_device_resume() call
>>>>> in amdgpu_pmops_thaw(), and skip amdgpu_device_ip_suspend() call in
>>>>> amdgpu_pci_shutdown()for hibernation.
>>>>> Initial tests show it's working fine for hibernation successful case.
>>>>> Should I switch to this implementation?
>>>> No idea. Alex and the KFD guys need to take a look at that.
>>>>
>>>>> But thaw() is also called to restore the GPU when hibernation is aborted
>>>>> due to some error in hibernation image creation stage. In this case,
>>>>> amdgpu_device_resume() is needed in thaw().
>>>>>
>>>>> So I need a method to check if hibernation is aborted or not to
>>>>> conditionally skip amdgpu_device_resume() in thaw(). Currently I don't
>>>>> know how to do this.
>>>> Yeah that approach here looks fishy to me, but I don't know how to properly fix it either.
>>>>
>>>> @Alex any idea?
>>> Yeah, I'm not sure how to handle that.  I don't see a way to avoid
>>> having all of the callbacks.  We could ideally skip some of the steps.
>>> Maybe we could optimize the freeze and thaw routines if we had some
>>> hint from the pm core about why we were getting called.  E.g., thaw
>>> after a failed hibernation restore.
>>>
>>> Alex
>>
>>
>> I just found pm_transition variable can be used to check if hibernation
>> is cancelled (PM_EVENT_RECOVER) or not(PM_EVENT_THAW) in thaw(). I just
>> need to export this variable in kernel.
>> https://github.com/torvalds/linux/blob/master/drivers/base/power/main.c#L64
>>
>> Provided pm_transition is available, should we skip
>> amdgpu_amdkfd_resume_process() only, or skip amdgpu_device_resume()
>> completely?
> 
> Hmmm.  Still not sure how best to handle this.  For entering
> hibernation, all we really need is freeze().  Once we are done with
> that we don't need thaw() or poweroff() for hibernation as we've
> already suspended in freeze() so there is nothing else to do.  For
> exiting hibernation, we need freeze() to suspend and then either
> thaw() (if the hibernation image is bad) or restore() (if the
> hibernation image is good) to resume.
> 

If pm_transition is available, we can keep thaw() as we have now and do
resume only if pm_transition =  PM_EVENT_RECOVER. shutdown() may check
in_s4 and do nothing.

Thanks,
Lijo


> Alex
> 
>>
>> Regards
>> Sam
>>
>>
>>>
>>>> Regards,
>>>> Christian.
>>>>
>>>>>
>>>>> Regards
>>>>> Sam
>>>>>
>>>>>
>>>>> On 2025/6/30 19:58, Christian König wrote:
>>>>>> On 30.06.25 12:41, Samuel Zhang wrote:
>>>>>>> The hibernation successful workflow:
>>>>>>> - prepare: evict VRAM and swapout GTT BOs
>>>>>>> - freeze
>>>>>>> - create the hibernation image in system memory
>>>>>>> - thaw: swapin and restore BOs
>>>>>> Why should a thaw happen here in between?
>>>>>>
>>>>>>> - complete
>>>>>>> - write hibernation image to disk
>>>>>>> - amdgpu_pci_shutdown
>>>>>>> - goto S5, turn off the system.
>>>>>>>
>>>>>>> During prepare stage of hibernation, VRAM and GTT BOs will be swapout to
>>>>>>> shmem. Then in thaw stage, all BOs will be swapin and restored.
>>>>>> That's not correct. This is done by the application starting again and not during thaw.
>>>>>>
>>>>>>> On server with 192GB VRAM * 8 dGPUs and 1.7TB system memory,
>>>>>>> the swapin and restore BOs takes too long (50 minutes) and it is not
>>>>>>> necessary since the follow-up stages does not use GPU.
>>>>>>>
>>>>>>> This patch is to skip BOs restore during thaw to reduce the hibernation
>>>>>>> time.
>>>>>> As far as I can see that doesn't make sense. The KFD processes need to be resumed here and that can't be skipped.
>>>>>>
>>>>>> Regards,
>>>>>> Christian.
>>>>>>
>>>>>>> Signed-off-by: Samuel Zhang <guoqing.zhang@amd.com>
>>>>>>> ---
>>>>>>>    drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 2 +-
>>>>>>>    drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c    | 2 ++
>>>>>>>    2 files changed, 3 insertions(+), 1 deletion(-)
>>>>>>>
>>>>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>>>>>>> index a8f4697deb1b..b550d07190a2 100644
>>>>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>>>>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>>>>>>> @@ -5328,7 +5328,7 @@ int amdgpu_device_resume(struct drm_device *dev, bool notify_clients)
>>>>>>>                amdgpu_virt_init_data_exchange(adev);
>>>>>>>                amdgpu_virt_release_full_gpu(adev, true);
>>>>>>>
>>>>>>> -            if (!adev->in_s0ix && !r && !adev->in_runpm)
>>>>>>> +            if (!adev->in_s0ix && !r && !adev->in_runpm && !adev->in_s4)
>>>>>>>                        r = amdgpu_amdkfd_resume_process(adev);
>>>>>>>        }
>>>>>>>
>>>>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
>>>>>>> index 571b70da4562..23b76e8ac2fd 100644
>>>>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
>>>>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
>>>>>>> @@ -2734,7 +2734,9 @@ static int amdgpu_pmops_poweroff(struct device *dev)
>>>>>>>    static int amdgpu_pmops_restore(struct device *dev)
>>>>>>>    {
>>>>>>>        struct drm_device *drm_dev = dev_get_drvdata(dev);
>>>>>>> +    struct amdgpu_device *adev = drm_to_adev(drm_dev);
>>>>>>>
>>>>>>> +    adev->in_s4 = false;
>>>>>>>        return amdgpu_device_resume(drm_dev, true);
>>>>>>>    }
>>>>>>>