Re: [Intel-gfx] [PATCH 13/27] drm/i915/guc: Ensure GuC schedule operations do not operate on child contexts

On 8/20/2021 15:44, Matthew Brost wrote:

In GuC parent-child contexts the parent context controls the scheduling, ensure only the parent does the scheduling operations.

Signed-off-by: Matthew Brost matthew.brost@intel.com

.../gpu/drm/i915/gt/uc/intel_guc_submission.c | 24 ++++++++++++++----- 1 file changed, 18 insertions(+), 6 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 dbcb9ab28a9a..00d54bb00bfb 100644 --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c @@ -320,6 +320,12 @@ static void decr_context_committed_requests(struct intel_context *ce) GEM_BUG_ON(ce->guc_state.number_committed_requests < 0); }

+static struct intel_context * +request_to_scheduling_context(struct i915_request *rq) +{

• return intel_context_to_parent(rq->context);

+}

• static bool context_guc_id_invalid(struct intel_context *ce) { return ce->guc_id.id == GUC_INVALID_LRC_ID;

@@ -1684,6 +1690,7 @@ static void __guc_context_sched_disable(struct intel_guc *guc,

GEM_BUG_ON(guc_id == GUC_INVALID_LRC_ID);

• GEM_BUG_ON(intel_context_is_child(ce)); trace_intel_context_sched_disable(ce);

  guc_submission_send_busy_loop(guc, action, ARRAY_SIZE(action),

@@ -1898,6 +1905,8 @@ static void guc_context_sched_disable(struct intel_context *ce) u16 guc_id; bool enabled;

• GEM_BUG_ON(intel_context_is_child(ce));
• if (submission_disabled(guc) || context_guc_id_invalid(ce) || !lrc_desc_registered(guc, ce->guc_id.id)) { spin_lock_irqsave(&ce->guc_state.lock, flags);

@@ -2286,6 +2295,8 @@ static void guc_signal_context_fence(struct intel_context *ce) { unsigned long flags;

• GEM_BUG_ON(intel_context_is_child(ce));
• spin_lock_irqsave(&ce->guc_state.lock, flags); clr_context_wait_for_deregister_to_register(ce); __guc_signal_context_fence(ce);

@@ -2315,7 +2326,7 @@ static void guc_context_init(struct intel_context *ce)

static int guc_request_alloc(struct i915_request *rq) {

• struct intel_context *ce = rq->context;

• struct intel_context *ce = request_to_scheduling_context(rq); struct intel_guc *guc = ce_to_guc(ce); unsigned long flags; int ret;

@@ -2358,11 +2369,12 @@ static int guc_request_alloc(struct i915_request *rq) * exhausted and return -EAGAIN to the user indicating that they can try * again in the future. *

• * There is no need for a lock here as the timeline mutex ensures at
  

• * most one context can be executing this code path at once. The
  

• * guc_id_ref is incremented once for every request in flight and
  

• * decremented on each retire. When it is zero, a lock around the
  

• * increment (in pin_guc_id) is needed to seal a race with unpin_guc_id.
  

• * There is no need for a lock here as the timeline mutex (or
  

• * parallel_submit mutex in the case of multi-lrc) ensures at most one
  

• * context can be executing this code path at once. The guc_id_ref is
  

Isn't that now two? One uni-LRC holding the timeline mutex and one multi-LRC holding the parallel submit mutex?

John.

• * incremented once for every request in flight and decremented on each
  

• * retire. When it is zero, a lock around the increment (in pin_guc_id)
  

• * is needed to seal a race with unpin_guc_id.
  

  */ if (atomic_add_unless(&ce->guc_id.ref, 1, 0)) goto out;