| Message ID | 20240804091851.122186-3-david@davidgow.net (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm/i915: Fix ttm small BAR placement handling | expand |
-----Original Message----- From: Intel-gfx <intel-gfx-bounces@lists.freedesktop.org> On Behalf Of David Gow Sent: Sunday, August 4, 2024 2:19 AM To: Christian König <ckoenig.leichtzumerken@gmail.com>; Somalapuram Amaranath <Amaranath.Somalapuram@amd.com>; Thomas Hellström <thomas.hellstrom@linux.intel.com>; De Marchi, Lucas <lucas.demarchi@intel.com>; Andi Shyti <andi.shyti@linux.intel.com>; Thomas Zimmermann <tzimmermann@suse.de> Cc: David Gow <david@davidgow.net>; Jani Nikula <jani.nikula@linux.intel.com>; Joonas Lahtinen <joonas.lahtinen@linux.intel.com>; Vivi, Rodrigo <rodrigo.vivi@intel.com>; Tvrtko Ursulin <tursulin@ursulin.net>; Ville Syrjälä <ville.syrjala@linux.intel.com>; intel-gfx@lists.freedesktop.org; dri-devel@lists.freedesktop.org; linux-kernel@vger.kernel.org Subject: [PATCH 2/2] drm/i915: Attempt to get pages without eviction first > > In commit a78a8da51b36 ("drm/ttm: replace busy placement with flags v6"), > __i915_ttm_get_pages was updated to use flags instead of the separate > 'busy' placement list. However, the behaviour was subtly changed. > Originally, the function would attempt to use the preferred placement > without eviction, and give an opportunity to restart the operation > before falling back to allowing eviction. > > This was unintentionally changed, as the preferred placement was not > given the TTM_PL_FLAG_DESIRED flag, and so eviction could be triggered > in that first pass. This caused thrashing, and a significant performance > regression on DG2 systems with small BAR. For example, Minecraft and > Team Fortress 2 would drop to single-digit framerates. > > Restore the original behaviour by marking the initial placement as > desired on that first attempt. Also, rework this to use a separate > struct ttm_palcement, as the individual placements are marked 'const', > so hot-patching the flags is even more dodgy than before. > > Thanks to Justin Brewer for bisecting this. > > Fixes: a78a8da51b36 ("drm/ttm: replace busy placement with flags v6") > Link: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/11255 > Signed-off-by: David Gow <david@davidgow.net> Thank you for the thorough write-up of this issue. Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com> -Jonathan Cavitt > --- > drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 12 +++++++----- > 1 file changed, 7 insertions(+), 5 deletions(-) > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c > index fb848fd8ba15..5c72462d1f57 100644 > --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c > +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c > @@ -778,13 +778,16 @@ static int __i915_ttm_get_pages(struct drm_i915_gem_object *obj, > .interruptible = true, > .no_wait_gpu = false, > }; > - int real_num_busy; > + struct ttm_placement initial_placement; > + struct ttm_place initial_place; > int ret; > > /* First try only the requested placement. No eviction. */ > - real_num_busy = placement->num_placement; > - placement->num_placement = 1; > - ret = ttm_bo_validate(bo, placement, &ctx); > + initial_placement.num_placement = 1; > + memcpy(&initial_place, placement->placement, sizeof(struct ttm_place)); > + initial_place.flags |= TTM_PL_FLAG_DESIRED; > + initial_placement.placement = &initial_place; > + ret = ttm_bo_validate(bo, &initial_placement, &ctx); > if (ret) { > ret = i915_ttm_err_to_gem(ret); > /* > @@ -799,7 +802,6 @@ static int __i915_ttm_get_pages(struct drm_i915_gem_object *obj, > * If the initial attempt fails, allow all accepted placements, > * evicting if necessary. > */ > - placement->num_placement = real_num_busy; > ret = ttm_bo_validate(bo, placement, &ctx); > if (ret) > return i915_ttm_err_to_gem(ret); > -- > 2.46.0 > >
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c index fb848fd8ba15..5c72462d1f57 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c @@ -778,13 +778,16 @@ static int __i915_ttm_get_pages(struct drm_i915_gem_object *obj, .interruptible = true, .no_wait_gpu = false, }; - int real_num_busy; + struct ttm_placement initial_placement; + struct ttm_place initial_place; int ret; /* First try only the requested placement. No eviction. */ - real_num_busy = placement->num_placement; - placement->num_placement = 1; - ret = ttm_bo_validate(bo, placement, &ctx); + initial_placement.num_placement = 1; + memcpy(&initial_place, placement->placement, sizeof(struct ttm_place)); + initial_place.flags |= TTM_PL_FLAG_DESIRED; + initial_placement.placement = &initial_place; + ret = ttm_bo_validate(bo, &initial_placement, &ctx); if (ret) { ret = i915_ttm_err_to_gem(ret); /* @@ -799,7 +802,6 @@ static int __i915_ttm_get_pages(struct drm_i915_gem_object *obj, * If the initial attempt fails, allow all accepted placements, * evicting if necessary. */ - placement->num_placement = real_num_busy; ret = ttm_bo_validate(bo, placement, &ctx); if (ret) return i915_ttm_err_to_gem(ret);
In commit a78a8da51b36 ("drm/ttm: replace busy placement with flags v6"), __i915_ttm_get_pages was updated to use flags instead of the separate 'busy' placement list. However, the behaviour was subtly changed. Originally, the function would attempt to use the preferred placement without eviction, and give an opportunity to restart the operation before falling back to allowing eviction. This was unintentionally changed, as the preferred placement was not given the TTM_PL_FLAG_DESIRED flag, and so eviction could be triggered in that first pass. This caused thrashing, and a significant performance regression on DG2 systems with small BAR. For example, Minecraft and Team Fortress 2 would drop to single-digit framerates. Restore the original behaviour by marking the initial placement as desired on that first attempt. Also, rework this to use a separate struct ttm_palcement, as the individual placements are marked 'const', so hot-patching the flags is even more dodgy than before. Thanks to Justin Brewer for bisecting this. Fixes: a78a8da51b36 ("drm/ttm: replace busy placement with flags v6") Link: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/11255 Signed-off-by: David Gow <david@davidgow.net> --- drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-)