Re: [RFC PATCH 42/42] HAX drm/i915/lmem: default userspace allocations to LMEM

Chris Wilson
2019-02-18T12:44:56Z

Quoting Chris Wilson (2019-02-14 16:13:18)
> Quoting Matthew Auld (2019-02-14 14:57:40)
> > Hack patch to default all userspace allocations to LMEM. Useful for
> > testing purposes.
> >
> > Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> > Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> > Cc: Abdiel Janulgue <abdiel.janulgue@linux.intel.com>
> > ---
> > drivers/gpu/drm/i915/i915_gem.c | 45 +++++++++++++++++++++++++++++++--
> > 1 file changed, 43 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> > index 3c86909d55b9..bd857f477ef9 100644
> > --- a/drivers/gpu/drm/i915/i915_gem.c
> > +++ b/drivers/gpu/drm/i915/i915_gem.c
> > @@ -641,7 +641,8 @@ i915_gem_create(struct drm_file *file,
> > u32 *handle_p)
> > {
> > struct drm_i915_gem_object *obj;
> > - int ret;
> > + intel_wakeref_t wakeref;
> > + int ret = 0;
> > u32 handle;
> >
> > size = roundup(size, PAGE_SIZE);
> > @@ -649,10 +650,50 @@ i915_gem_create(struct drm_file *file,
> > return -EINVAL;
> >
> > /* Allocate the new object */
> > - obj = i915_gem_object_create(dev_priv, size);
> > + if (HAS_LMEM(dev_priv))
> > + obj = i915_gem_object_create_lmem(dev_priv, size, 0);
> > + else
> > + obj = i915_gem_object_create(dev_priv, size);
> > if (IS_ERR(obj))
> > return PTR_ERR(obj);
> >
> > + if (i915_gem_object_is_lmem(obj)) {
> > + struct i915_gem_context *ctx;
> > +
> > + /* XXX: we should prob use the blitter context for this? */
>
> Or the kernel_context which is setup for emitting without taking
> struct_mutex...

Actually doing this async (i.e. not blocking object creation due to
clear) requires us to be sure that the cpu access via mmap has a sync
point. pread, mmap_ggtt does, but mmap_(wb|wc) does not currently, and
we would be reliant on userspace doing a set-domain first in order for
them not to see stale buffer content.

Also I have this penciled in to enable buffer pools (e.g. !llc would
dearly love to keep WC pages around before giving them back to the
system).

Hmm,
-Chris