Re: [PATCH v3 0/5] Improving the worst case TTM large allocation latency

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

On 08.10.25 13:53, Tvrtko Ursulin wrote:
> Disclaimer:
> Please note that as this series includes a patch which touches a good number of
> drivers I will only copy everyone in the cover letter and the respective patch.
> Assumption is people are subscribed to dri-devel so can look at the whole series
> there. I know someone is bound to complain for both the case when everyone is
> copied on everything for getting too much email, and also for this other case.
> So please be flexible.
> 
> Description:
> 
> All drivers which use the TTM pool allocator end up requesting large order
> allocations when allocating large buffers. Those can be slow due memory pressure
> and so add latency to buffer creation. But there is often also a size limit
> above which contiguous blocks do not bring any performance benefits. This series
> allows drivers to say when it is okay for the TTM to try a bit less hard.
> 
> We do this by allowing drivers to specify this cut off point when creating the
> TTM device and pools. Allocations above this size will skip direct reclaim so
> under memory pressure worst case latency will improve. Background reclaim is
> still kicked off and both before and after the memory pressure all the TTM pool
> buckets remain to be used as they are today.
> 
> This is especially interesting if someone has configured MAX_PAGE_ORDER to
> higher than the default. And even with the default, with amdgpu for example,
> the last patch in the series makes use of the new feature by telling TTM that
> above 2MiB we do not expect performance benefits. Which makes TTM not try direct
> reclaim for the top bucket (4MiB).
> 
> End result is TTM drivers become a tiny bit nicer mm citizens and users benefit
> from better worst case buffer creation latencies. As a side benefit we get rid
> of two instances of those often very unreadable mutliple nameless booleans
> function signatures.
> 
> If this sounds interesting and gets merge the invidual drivers can follow up
> with patches configuring their thresholds.
> 
> v2:
>  * Christian suggested to pass in the new data by changing the function signatures.
> 
> v3:
>  * Moved ttm pool helpers into new ttm_pool_internal.h. (Christian)

Patch #3 is Acked-by: Christian König <christian.koenig@amd.com>.

The rest is Reviewed-by: Christian König <christian.koenig@amd.com>

Thanks,
Christian.

> 
> v1 thread:
> https://lore.kernel.org/dri-devel/20250919131127.90932-1-tvrtko.ursulin@igalia.com/
> 
> Cc: Alex Deucher <alexander.deucher@amd.com>
> Cc: Christian König <christian.koenig@amd.com>
> Cc: Danilo Krummrich <dakr@kernel.org>
> Cc: Dave Airlie <airlied@redhat.com>
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: Lucas De Marchi <lucas.demarchi@intel.com>
> Cc: Lyude Paul <lyude@redhat.com>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Maxime Ripard <mripard@kernel.org>
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Cc: Sui Jingfeng <suijingfeng@loongson.cn>
> Cc: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: Zack Rusin <zack.rusin@broadcom.com>
> 
> Tvrtko Ursulin (5):
>   drm/ttm: Add getter for some pool properties
>   drm/ttm: Replace multiple booleans with flags in pool init
>   drm/ttm: Replace multiple booleans with flags in device init
>   drm/ttm: Allow drivers to specify maximum beneficial TTM pool size
>   drm/amdgpu: Configure max beneficial TTM pool allocation order
> 
>  drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c       |  7 +--
>  drivers/gpu/drm/drm_gem_vram_helper.c         |  2 +-
>  drivers/gpu/drm/i915/intel_region_ttm.c       |  2 +-
>  drivers/gpu/drm/loongson/lsdc_ttm.c           |  2 +-
>  drivers/gpu/drm/nouveau/nouveau_ttm.c         |  4 +-
>  drivers/gpu/drm/qxl/qxl_ttm.c                 |  2 +-
>  drivers/gpu/drm/radeon/radeon_ttm.c           |  4 +-
>  drivers/gpu/drm/ttm/tests/ttm_bo_test.c       | 16 +++----
>  .../gpu/drm/ttm/tests/ttm_bo_validate_test.c  |  2 +-
>  drivers/gpu/drm/ttm/tests/ttm_device_test.c   | 31 +++++--------
>  drivers/gpu/drm/ttm/tests/ttm_kunit_helpers.c | 22 ++++-----
>  drivers/gpu/drm/ttm/tests/ttm_kunit_helpers.h |  7 +--
>  drivers/gpu/drm/ttm/tests/ttm_pool_test.c     | 23 +++++-----
>  drivers/gpu/drm/ttm/ttm_device.c              |  7 ++-
>  drivers/gpu/drm/ttm/ttm_pool.c                | 45 +++++++++++--------
>  drivers/gpu/drm/ttm/ttm_pool_internal.h       | 24 ++++++++++
>  drivers/gpu/drm/ttm/ttm_tt.c                  | 10 +++--
>  drivers/gpu/drm/vmwgfx/vmwgfx_drv.c           |  4 +-
>  drivers/gpu/drm/xe/xe_device.c                |  2 +-
>  include/drm/ttm/ttm_device.h                  |  2 +-
>  include/drm/ttm/ttm_pool.h                    | 13 +++---
>  21 files changed, 125 insertions(+), 106 deletions(-)
>  create mode 100644 drivers/gpu/drm/ttm/ttm_pool_internal.h
>