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

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Message-ID: <7346d42b-3ad7-4170-900f-73d8ed356f71@linux.intel.com>
Date: Wed, 26 Nov 2025 16:34:16 +0100
From: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
To: Christian König <christian.koenig@....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

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.

Kind regards,
~Maarten Lankhorst