Re: [Intel-gfx] [PATCH 22/26] drm/i915/guc: Handle errors in multi-lrc requests

[Matthew Brost <matthew.brost@intel.com>]

On Tue, Oct 12, 2021 at 02:56:36PM -0700, John Harrison wrote:
> On 10/4/2021 15:06, Matthew Brost wrote:
> > If an error occurs in the front end when multi-lrc requests are getting
> > generated we need to skip these in the backend but we still need to
> > emit the breadcrumbs seqno. An issues arises because with multi-lrc
> > breadcrumbs there is a handshake between the parent and children to make
> > forward progress. If all the requests are not present this handshake
> > doesn't work. To work around this, if multi-lrc request has an error we
> > skip the handshake but still emit the breadcrumbs seqno.
> > 
> > v2:
> >   (John Harrison)
> >    - Add comment explaining the skipping of the handshake logic
> >    - Fix typos in the commit message
> > 
> > Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> > ---
> >   .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 71 ++++++++++++++++++-
> >   1 file changed, 68 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > index 83b0d2a114af..05e8b199e4ce 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > @@ -4072,8 +4072,8 @@ static int emit_bb_start_child_no_preempt_mid_batch(struct i915_request *rq,
> >   }
> >   static u32 *
> > -emit_fini_breadcrumb_parent_no_preempt_mid_batch(struct i915_request *rq,
> > -						 u32 *cs)
> > +__emit_fini_breadcrumb_parent_no_preempt_mid_batch(struct i915_request *rq,
> > +						   u32 *cs)
> >   {
> >   	struct intel_context *ce = rq->context;
> >   	u8 i;
> > @@ -4101,6 +4101,46 @@ emit_fini_breadcrumb_parent_no_preempt_mid_batch(struct i915_request *rq,
> >   				  get_children_go_addr(ce),
> >   				  0);
> > +	return cs;
> > +}
> > +
> > +/*
> > + * If this true, a submission of multi-lrc requests had an error and the
> > + * requests need to be skipped. The front end (execuf IOCTL) should've called
> > + * i915_request_skip which squashes the BB but we still need to emit the fini
> > + * breadrcrumbs seqno write. At this point we don't know how many of the
> > + * requests in the multi-lrc submission were generated so we can't do the
> > + * handshake between the parent and children (e.g. if 4 requests should be
> > + * generated but 2nd hit an error only 1 would be seen by the GuC backend).
> > + * Simply skip the handshake, but still emit the breadcrumbd seqno, if an error
> > + * has occurred on any of the requests in submission / relationship.
> > + */
> > +static inline bool skip_handshake(struct i915_request *rq)
> > +{
> > +	return test_bit(I915_FENCE_FLAG_SKIP_PARALLEL, &rq->fence.flags);
> > +}
> > +
> > +static u32 *
> > +emit_fini_breadcrumb_parent_no_preempt_mid_batch(struct i915_request *rq,
> > +						 u32 *cs)
> > +{
> > +	struct intel_context *ce = rq->context;
> > +
> > +	GEM_BUG_ON(!intel_context_is_parent(ce));
> > +
> > +	if (unlikely(skip_handshake(rq))) {
> > +		/*
> > +		 * NOP everything in
> > +		 * __emit_fini_breadcrumb_parent_no_preempt_mid_batch, the -6
> The line wrapping makes this look confusing. It seems like the function name
> should fit on the line before. Even if it is a few characters over (although
> the limit is now 100 not 80, I think), the checkpatch warning is worth the
> readability of the code.
> 

My vi setting wrap everything as 80 but agree it would be more readable
if __emit_fini_breadcrumb_parent_no_preempt_mid_batch was on the
previous line.

> > +		 * comes of the length emission below.
> -> comes from the length of the emits below.
>

Sure. Will fix.

Matt

> John.
> 
> > +		 */
> > +		memset(cs, 0, sizeof(u32) *
> > +		       (ce->engine->emit_fini_breadcrumb_dw - 6));
> > +		cs += ce->engine->emit_fini_breadcrumb_dw - 6;
> > +	} else {
> > +		cs = __emit_fini_breadcrumb_parent_no_preempt_mid_batch(rq, cs);
> > +	}
> > +
> >   	/* Emit fini breadcrumb */
> >   	cs = gen8_emit_ggtt_write(cs,
> >   				  rq->fence.seqno,
> > @@ -4117,7 +4157,8 @@ emit_fini_breadcrumb_parent_no_preempt_mid_batch(struct i915_request *rq,
> >   }
> >   static u32 *
> > -emit_fini_breadcrumb_child_no_preempt_mid_batch(struct i915_request *rq, u32 *cs)
> > +__emit_fini_breadcrumb_child_no_preempt_mid_batch(struct i915_request *rq,
> > +						  u32 *cs)
> >   {
> >   	struct intel_context *ce = rq->context;
> >   	struct intel_context *parent = intel_context_to_parent(ce);
> > @@ -4144,6 +4185,30 @@ emit_fini_breadcrumb_child_no_preempt_mid_batch(struct i915_request *rq, u32 *cs
> >   	*cs++ = get_children_go_addr(parent);
> >   	*cs++ = 0;
> > +	return cs;
> > +}
> > +
> > +static u32 *
> > +emit_fini_breadcrumb_child_no_preempt_mid_batch(struct i915_request *rq,
> > +						u32 *cs)
> > +{
> > +	struct intel_context *ce = rq->context;
> > +
> > +	GEM_BUG_ON(!intel_context_is_child(ce));
> > +
> > +	if (unlikely(skip_handshake(rq))) {
> > +		/*
> > +		 * NOP everything in
> > +		 * __emit_fini_breadcrumb_child_no_preempt_mid_batch, the -6
> > +		 * comes from the length the emission below.
> > +		 */
> > +		memset(cs, 0, sizeof(u32) *
> > +		       (ce->engine->emit_fini_breadcrumb_dw - 6));
> > +		cs += ce->engine->emit_fini_breadcrumb_dw - 6;
> > +	} else {
> > +		cs = __emit_fini_breadcrumb_child_no_preempt_mid_batch(rq, cs);
> > +	}
> > +
> >   	/* Emit fini breadcrumb */
> >   	cs = gen8_emit_ggtt_write(cs,
> >   				  rq->fence.seqno,
>