Re: [RFC PATCH v3 2/4] drm: Create DRM_IOCTL_GET_RESET

["Christian König" <christian.koenig@amd.com>]

Am 22.06.23 um 10:22 schrieb Pekka Paalanen:
> On Wed, 21 Jun 2023 13:33:56 -0300
> André Almeida <andrealmeid@igalia.com> wrote:
>
>> Em 21/06/2023 05:09, Pekka Paalanen escreveu:
>>> On Tue, 20 Jun 2023 21:57:17 -0300
>>> André Almeida <andrealmeid@igalia.com> wrote:
>>>    
>>>> Create a new DRM ioctl operation to get the numbers of resets for a
>>>> given context. The numbers reflect just the resets that happened after
>>>> the context was created, and not since the machine was booted.
>>>>
>>>> Create a debugfs interface to make easier to test the API without real
>>>> resets.
>>>>
>>>> Signed-off-by: André Almeida <andrealmeid@igalia.com>
>>>> ---
>>>>    drivers/gpu/drm/drm_debugfs.c |  2 ++
>>>>    drivers/gpu/drm/drm_ioctl.c   | 58 +++++++++++++++++++++++++++++++++++
>>>>    include/drm/drm_device.h      |  3 ++
>>>>    include/drm/drm_drv.h         |  3 ++
>>>>    include/uapi/drm/drm.h        | 21 +++++++++++++
>>>>    include/uapi/drm/drm_mode.h   | 15 +++++++++
>>>>    6 files changed, 102 insertions(+)
>>> ...
>>>    
>>>> diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h
>>>> index a87bbbbca2d4..a84559aa0d77 100644
>>>> --- a/include/uapi/drm/drm.h
>>>> +++ b/include/uapi/drm/drm.h
>>>> @@ -1169,6 +1169,27 @@ extern "C" {
>>>>     */
>>>>    #define DRM_IOCTL_MODE_GETFB2		DRM_IOWR(0xCE, struct drm_mode_fb_cmd2)
>>>>    
>>>> +/**
>>>> + * DRM_IOCTL_GET_RESET - Get information about device resets
>>>> + *
>>>> + * This operation requests from the device information about resets. It should
>>>> + * consider only resets that happens after the context is created, therefore,
>>>> + * the counter should be zero during context creation.
>>>> + *
>>>> + * dev_reset_count tells how many resets have happened on this device, and
>>>> + * ctx_reset_count tells how many of such resets were caused by this context.
>>>> + *
>>>> + * Flags can be used to tell if a reset is in progress, and userspace should
>>>> + * wait until it's not in progress anymore to be able to create a new context;
>>>> + * and to tell if the VRAM is considered lost. There's no safe way to clean this
>>>> + * flag so if a context see this flag set, it should be like that until the end
>>>> + * of the context.
>>> Is "this flag" the VRAM_LOST? Or any flag?
>>>
>>> Does this mean that not all resets are fatal to the context? Is there
>>> any kind of reset that should not be fatal to a context? All the
>>> rendering APIs seem to assume that any reset is fatal and the context
>>> must be destroyed.
>> I got this flag from the `AMDGPU_CTX_OP_QUERY_STATE2` operation, and
>> it's used to notify that the reset was fatal for a giving context,
>> although the idea of non-fatal resets seems to be a bit controversial
>> for now, so I think it will be better if I leave this flag for latter
>> improvements of the API.
> Which flag is "this flag"? There are RESET_IN_PROGRESS and VRAM_LOST.
> Both are fine by me to exist.
>
> I think I made a wrong conclusion here. Somehow I read that it would be
> possible to have a reset happen, and if VRAM is not lost, then the
> context could work again.

Yeah, that's exactly what AMD tries to do.

And no, I'm absolutely not keen about that idea.

Regards,
Christian.

> Should there be some wording added to say the context is permanently
> broken on any kind of reset? Or is that for UMD to decide?
>
>
> Thanks,
> pq
>
>>>    
>>>> + */
>>>> +#define DRM_IOCTL_GET_RESET		DRM_IOWR(0xCF, struct drm_get_reset)
>>>> +
>>>> +#define DRM_RESET_IN_PROGRESS	0x1
>>>> +#define DRM_RESET_VRAM_LOST	0x2
>>> Ok, so the dmabuf lost is being communicated here, but how would a
>>> userspace process know on which device a dmabuf resides on?
>>>
>>> Let's assume process A uses device 1 to draw, exports a dmabuf, sends
>>> it to process B which imports it to device 2. Device 1 resets and loses
>>> VRAM contents. How would process B notice that the dmabuf is lost when
>>> it never touches device 1 itself?
>>>    
>>>> +
>>>>    /*
>>>>     * Device specific ioctls should only be in their respective headers
>>>>     * The device specific ioctl range is from 0x40 to 0x9f.
>>>> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
>>>> index 43691058d28f..c3257bd1af9c 100644
>>>> --- a/include/uapi/drm/drm_mode.h
>>>> +++ b/include/uapi/drm/drm_mode.h
>>>> @@ -1308,6 +1308,21 @@ struct drm_mode_rect {
>>>>    	__s32 y2;
>>>>    };
>>>>    
>>>> +/**
>>>> + * struct drm_get_reset - Get information about a DRM device resets
>>>> + * @ctx_id: the context id to be queried about resets
>>>> + * @flags: flags
>>>> + * @dev_reset_count: global counter of resets for a given DRM device
>>>> + * @ctx_reset_count: of all the resets counted by this device, how many were
>>>> + * caused by this context.
>>>> + */
>>>> +struct drm_get_reset {
>>>> +	__u32 ctx_id;
>>>> +	__u32 flags;
>>>> +	__u64 dev_reset_count;
>>>> +	__u64 ctx_reset_count;
>>>> +};
>>>> +
>>>>    #if defined(__cplusplus)
>>>>    }
>>>>    #endif
>>> Thanks,
>>> pq