Re: [Intel-gfx] [PATCH] drm/i915/gem: Drop relocation support on all new hardware (v6)

["Zbigniew Kempczyński" <zbigniew.kempczynski@intel.com>]

On Wed, Mar 17, 2021 at 09:41:46AM -0500, Jason Ekstrand wrote:
> I should probably have said that the reviews are on v5 and it's very
> different in v6 so they should probably be considered dropped until
> re-confirmed.

You're checking relocation_count early in do_execbuffer() so imo there's
no option to pass execbuf with relocations now.

I keep my r-b.

--
Zbigniew

> 
> On Wed, Mar 17, 2021 at 9:39 AM Jason Ekstrand <jason@jlekstrand.net> wrote:
> >
> > The Vulkan driver in Mesa for Intel hardware never uses relocations if
> > it's running on a version of i915 that supports at least softpin which
> > all versions of i915 supporting Gen12 do.  On the OpenGL side, Gen12+ is
> > only supported by iris which never uses relocations.  The older i965
> > driver in Mesa does use relocations but it only supports Intel hardware
> > through Gen11 and has been deprecated for all hardware Gen9+.  The
> > compute driver also never uses relocations.  This only leaves the media
> > driver which is supposed to be switching to softpin going forward.
> > Making softpin a requirement for all future hardware seems reasonable.
> >
> > There is one piece of hardware enabled by default in i915: RKL which was
> > enabled by e22fa6f0a976 which has not yet landed in drm-next so this
> > almost but not really a userspace API change for RKL.  If it becomes a
> > problem, we can always add !IS_ROCKETLAKE(eb->i915) to the condition.
> >
> > Rejecting relocations starting with newer Gen12 platforms has the
> > benefit that we don't have to bother supporting it on platforms with
> > local memory.  Given how much CPU touching of memory is required for
> > relocations, not having to do so on platforms where not all memory is
> > directly CPU-accessible carries significant advantages.
> >
> > v2 (Jason Ekstrand):
> >  - Allow TGL-LP platforms as they've already shipped
> >
> > v3 (Jason Ekstrand):
> >  - WARN_ON platforms with LMEM support in case the check is wrong
> >
> > v4 (Jason Ekstrand):
> >  - Call out Rocket Lake in the commit message
> >
> > v5 (Jason Ekstrand):
> >  - Drop the HAS_LMEM check as it's already covered by the version check
> >
> > v6 (Jason Ekstrand):
> >  - Move the check to eb_validate_vma() with all the other exec_object
> >    validation checks.
> >
> > Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
> > Reviewed-by: Zbigniew Kempczyński <zbigniew.kempczynski@intel.com>
> > Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> > index 99772f37bff60..c082fb0bef330 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> > @@ -483,6 +483,13 @@ eb_validate_vma(struct i915_execbuffer *eb,
> >                 struct drm_i915_gem_exec_object2 *entry,
> >                 struct i915_vma *vma)
> >  {
> > +       /* Relocations are disallowed for all platforms after TGL-LP.  This
> > +        * also covers all platforms with local memory.
> > +        */
> > +       if (entry->relocation_count &&
> > +           INTEL_GEN(eb->i915) >= 12 && !IS_TIGERLAKE(eb->i915))
> > +               return -EINVAL;
> > +
> >         if (unlikely(entry->flags & eb->invalid_flags))
> >                 return -EINVAL;
> >
> > --
> > 2.29.2
> >
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