Re: [PATCH] drm/i915: Skip context_barrier emission for unused contexts

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On 06/06/2019 10:09, Chris Wilson wrote:
Quoting Tvrtko Ursulin (2019-06-05 11:40:27)

On 04/06/2019 16:24, Chris Wilson wrote:
The intent was to skip unused HW contexts by checking ce->state.
However, this only works for execlists where the ppGTT pointers is
stored inside the HW context. For gen7, the ppGTT is alongside the
logical state and must be updated on all active engines but, crucially,
only on active engines. As we need different checks, and to keep
context_barrier_task() agnostic, pass in the predicate.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=110836
Fixes: 62c8e423450d ("drm/i915: Skip unused contexts for context_barrier_task()")
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
---
   drivers/gpu/drm/i915/gem/i915_gem_context.c   | 15 ++++++++++++++-
   .../drm/i915/gem/selftests/i915_gem_context.c | 19 +++++++++++++++----
   2 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
index 08721ef62e4e..6819b598d226 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
@@ -902,6 +902,7 @@ static void cb_retire(struct i915_active *base)
   I915_SELFTEST_DECLARE(static intel_engine_mask_t context_barrier_inject_fault);
   static int context_barrier_task(struct i915_gem_context *ctx,
                               intel_engine_mask_t engines,
+                             bool (*skip)(struct intel_context *ce, void *data),
                               int (*emit)(struct i915_request *rq, void *data),
                               void (*task)(void *data),
                               void *data)
@@ -931,7 +932,10 @@ static int context_barrier_task(struct i915_gem_context *ctx,
                       break;
               }
- if (!(ce->engine->mask & engines) || !ce->state)
+             if (!(ce->engine->mask & engines))
+                     continue;
+
+             if (skip && skip(ce, data))
                       continue;
rq = intel_context_create_request(ce);
@@ -1058,6 +1062,14 @@ static int emit_ppgtt_update(struct i915_request *rq, void *data)
       return 0;
   }
+static bool skip_ppgtt_update(struct intel_context *ce, void *data)
+{
+     if (HAS_LOGICAL_RING_CONTEXTS(ce->engine->i915))
+             return !ce->state;
+     else
+             return !atomic_read(&ce->pin_count);

Would "return !atomic_read(&ce->pin_count) || !ce->state;" work and
avoid the somewhat irky HAS_LOGICAL_RING_CONTEXTS check?

No, because we need the barrier on gen7 !rcs which doesn't have
ce->state (but does need to switch mm).

That's not the path which would be covered by !atomic_read(&ce->pin_count) ?

Regards,

Tvrtko
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