Re: [PATCH] drm/xe: Attempt to bring bos back to VRAM after eviction

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On Fri, 2025-08-29 at 09:42 +0200, Maarten Lankhorst wrote:
> Hey,
> 
> Den 2025-08-28 kl. 17:42, skrev Thomas Hellström:
> > VRAM+TT bos that are evicted from VRAM to TT may remain in
> > TT also after a revalidation following eviction or suspend.
> > 
> > This manifests itself as applications becoming sluggish
> > after buffer objects get evicted or after a resume from
> > suspend or hibernation.
> > 
> > If the bo supports placement in both VRAM and TT, and
> > we are on DGFX, mark the TT placement as fallback. This means
> > that it is tried only after VRAM + eviction.
> > 
> > This flaw has probably been present since the xe module was
> > upstreamed but use a Fixes: commit below where backporting is
> > likely to be simple. For earlier versions we need to open-
> > code the fallback algorithm in the driver.
> > 
> > Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/5995
> > Fixes: a78a8da51b36 ("drm/ttm: replace busy placement with flags
> > v6")
> I'd say it this closes a bug in the original driver, although
> effectively v6.8 is no longer supported anyway.
> 
> Should DESIRED also be set on the add_vram flags?

It looks for me from the TTM code that TTM then *skips* the placement
when doing a second pass with evictions.

So that's not really what we want IMO.

/Thomas

> 
> > Cc: Matthew Brost <matthew.brost@intel.com>
> > Cc: Matthew Auld <matthew.auld@intel.com>
> > Cc: <stable@vger.kernel.org> # v6.9+
> > Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> > ---
> >  drivers/gpu/drm/xe/xe_bo.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/xe/xe_bo.c
> > b/drivers/gpu/drm/xe/xe_bo.c
> > index 4faf15d5fa6d..64dea4e478bd 100644
> > --- a/drivers/gpu/drm/xe/xe_bo.c
> > +++ b/drivers/gpu/drm/xe/xe_bo.c
> > @@ -188,6 +188,8 @@ static void try_add_system(struct xe_device
> > *xe, struct xe_bo *bo,
> >  
> >  		bo->placements[*c] = (struct ttm_place) {
> >  			.mem_type = XE_PL_TT,
> > +			.flags = (IS_DGFX(xe) && (bo_flags &
> > XE_BO_FLAG_VRAM_MASK)) ?
> > +			TTM_PL_FLAG_FALLBACK : 0,
> >  		};
> >  		*c += 1;
> >  	}
> 
> Kind regards,
> ~Maarten Lankhorst