linux-kernel - Re: [PATCH v3 19/28] drm/ttm: rework pipelined eviction fence handling

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Message-ID: <cc43a512-b979-4c11-a413-ab5108dab466@amd.com>
Date: Wed, 26 Nov 2025 16:36:06 +0100
From: Christian König <christian.koenig@....com>
To: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@....com>,
 Huang Rui <ray.huang@....com>, Matthew Auld <matthew.auld@...el.com>,
 Matthew Brost <matthew.brost@...el.com>, Maxime Ripard <mripard@...nel.org>,
 Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, Sumit Semwal <sumit.semwal@...aro.org>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 linux-media@...r.kernel.org, linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH v3 19/28] drm/ttm: rework pipelined eviction fence
 handling

On 11/26/25 16:34, Maarten Lankhorst wrote:
> Hey,
> 
> Den 2025-11-21 kl. 16:12, skrev Christian König:
>> On 11/21/25 11:12, Pierre-Eric Pelloux-Prayer wrote:
>>> Until now ttm stored a single pipelined eviction fence which means
>>> drivers had to use a single entity for these evictions.
>>>
>>> To lift this requirement, this commit allows up to 8 entities to
>>> be used.
>>>
>>> Ideally a dma_resv object would have been used as a container of
>>> the eviction fences, but the locking rules makes it complex.
>>> dma_resv all have the same ww_class, which means "Attempting to
>>> lock more mutexes after ww_acquire_done." is an error.
>>>
>>> One alternative considered was to introduced a 2nd ww_class for
>>> specific resv to hold a single "transient" lock (= the resv lock
>>> would only be held for a short period, without taking any other
>>> locks).
>>>
>>> The other option, is to statically reserve a fence array, and
>>> extend the existing code to deal with N fences, instead of 1.
>>>
>>> The driver is still responsible to reserve the correct number
>>> of fence slots.
>>>
>>> ---
>>> v2:
>>> - simplified code
>>> - dropped n_fences
>>> - name changes
>>> v3: use ttm_resource_manager_cleanup
>>> ---
>>>
>>> Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@....com>
>>
>> Reviewed-by: Christian König <christian.koenig@....com>
>>
>> Going to push separately to drm-misc-next on Monday.
>>
> Pushing this broke drm-tip, the amd driver fails to build, as it's not using the eviction_fences array.

Thanks for the note! But hui? We changed amdgpu to not touch the move fence.

Give me a second.

Thanks,
Christian.

> 
> Kind regards,
> ~Maarten Lankhorst