I should have admitted defeat long ago as there has been a rare but persistent error on Sandybridge where semaphore signaling did not propagate to the waiter, leading to a GPU hang.
With the work on fence signaling for v4.9, the impact of using CPU driven signaling was greatly reduced wrt to the latency of GPU semaphores, though without logical rings support, the benefit of reordering work to avoid bubbles is not realised (i.e. as it stands fence signaling is just a slower, more costly version of HW semaphores; but works more consistently). As a rough indicator of the difference, with semaphores: Sequential (3 engines, 1 processes): average 5.470us per cycle [expected 4.988us] w/o semaphores: Sequential (3 engines, 1 processes): average 15.771us per cycle [expected 4.923us] In comparison, v3.4: with semaphores: Sequential (3 engines, 1 processes): average 16.066us per cycle [expected 11.842us] w/o semaphores: Sequential (3 engines, 1 processes): average 23.460us per cycle [expected 11.839us] Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=54226 #and 100+ dupes Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk> Cc: Joonas Lahtinen <joonas.lahti...@linux.intel.com> Acked-by: Mika Kuoppala <mika.kuopp...@linux.intel.com> Reviewed-by: Joonas Lahtinen <joonas.lahti...@linux.intel.com --- drivers/gpu/drm/i915/i915_gem.c | 10 +--------- 1 file changed, 1 insertion(+), 9 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index d470e10b2edd..d53bb8e872ba 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -4999,20 +4999,12 @@ int i915_gem_init_hw(struct drm_i915_private *dev_priv) bool intel_sanitize_semaphores(struct drm_i915_private *dev_priv, int value) { - if (INTEL_GEN(dev_priv) < 6) - return false; - - /* TODO: make semaphores and Execlists play nicely together */ - if (HAS_EXECLISTS(dev_priv)) + if (!IS_GEN7(dev_priv)) return false; if (value >= 0) return value; - /* Enable semaphores on SNB when IO remapping is off */ - if (IS_GEN6(dev_priv) && intel_vtd_active()) - return false; - return true; } -- 2.15.0 _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx
