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

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.

•  * comes of the length emission below.
  

-> comes from the length of the emits below.

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,