-----Original Message----- From: Intel-gfx <[email protected]> On Behalf Of David Gow Sent: Sunday, August 4, 2024 2:19 AM To: Christian König <[email protected]>; Somalapuram Amaranath <[email protected]>; Thomas Hellström <[email protected]>; De Marchi, Lucas <[email protected]>; Andi Shyti <[email protected]>; Thomas Zimmermann <[email protected]> Cc: David Gow <[email protected]>; Jani Nikula <[email protected]>; Joonas Lahtinen <[email protected]>; Vivi, Rodrigo <[email protected]>; Tvrtko Ursulin <[email protected]>; Ville Syrjälä <[email protected]>; [email protected]; [email protected]; [email protected] Subject: [PATCH 1/2] drm/i915: Allow evicting to use the requested placement > > In commit a78a8da51b36 ("drm/ttm: replace busy placement with flags v6"), > the old system of having a separate placement list (for placements > which should be used without eviction) and a 'busy' placement list (for > placements which should be attempted if eviction is required) was > replaced with a new one where placements could be marked 'FALLBACK' (to > be attempted if eviction is required) or 'DESIRED' (to be attempted > first, but not if eviction is required). > > i915 had always included the requested placement in the list of > 'busy' placements: i.e., the placement could be used either if eviction > is required or not. But when the new system was put in place, the > requested (first) placement was marked 'DESIRED', so would never be used > if eviction became necessary. While a bug in the original commit > prevented this flag from working, when this was fixed in > 4a0e7b3c ("drm/i915: fix applying placement flag"), it caused long hangs > on DG2 systems with small BAR. > > Don't mark the requested placement DESIRED (or FALLBACK), allowing it to > be used in both situations. This matches the old behaviour, and resolves > the hangs. > > Thanks to Justin Brewer for bisecting the issue. > > Fixes: a78a8da51b36 ("drm/ttm: replace busy placement with flags v6") > Fixes: 4a0e7b3c3753 ("drm/i915: fix applying placement flag") > Link: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/11255 > Signed-off-by: David Gow <[email protected]>
Thank you for the thorough write-up of this issue. Reviewed-by: Jonathan Cavitt <[email protected]> -Jonathan Cavitt > --- > drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 1 - > 1 file changed, 1 deletion(-) > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c > b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c > index e6f177183c0f..fb848fd8ba15 100644 > --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c > +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c > @@ -165,7 +165,6 @@ i915_ttm_placement_from_obj(const struct > drm_i915_gem_object *obj, > i915_ttm_place_from_region(num_allowed ? obj->mm.placements[0] : > obj->mm.region, &places[0], obj->bo_offset, > obj->base.size, flags); > - places[0].flags |= TTM_PL_FLAG_DESIRED; > > /* Cache this on object? */ > for (i = 0; i < num_allowed; ++i) { > -- > 2.46.0 > >
