drm/i915/perf: better pipeline aged/aging tail updates

This updates the tail pointer race workaround handling to updating the
'aged' pointer before looking to start aging a new one. There's the
possibility that there is already new data available and so we can
immediately start aging a new pointer without having to first wait for a
later hrtimer callback (and then another to age).

Signed-off-by: Robert Bragg <robert@sixbynine.org>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170511154345.962-8-lionel.g.landwerlin@intel.com
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
index 957b959..4d31b70 100644 (file)
--- a/drivers/gpu/drm/i915/i915_perf.c
+++ b/drivers/gpu/drm/i915/i915_perf.c
@@ -391,6 +391,29 @@ static bool gen7_oa_buffer_check_unlocked(struct drm_i915_private *dev_priv)
 
        now = ktime_get_mono_fast_ns();
 
+       /* Update the aged tail
+        *
+        * Flip the tail pointer available for read()s once the aging tail is
+        * old enough to trust that the corresponding data will be visible to
+        * the CPU...
+        *
+        * Do this before updating the aging pointer in case we may be able to
+        * immediately start aging a new pointer too (if new data has become
+        * available) without needing to wait for a later hrtimer callback.
+        */
+       if (aging_tail != INVALID_TAIL_PTR &&
+           ((now - dev_priv->perf.oa.oa_buffer.aging_timestamp) >
+            OA_TAIL_MARGIN_NSEC)) {
+               aged_idx ^= 1;
+               dev_priv->perf.oa.oa_buffer.aged_tail_idx = aged_idx;
+
+               aged_tail = aging_tail;
+
+               /* Mark that we need a new pointer to start aging... */
+               dev_priv->perf.oa.oa_buffer.tails[!aged_idx].offset = INVALID_TAIL_PTR;
+               aging_tail = INVALID_TAIL_PTR;
+       }
+
        /* Update the aging tail
         *
         * We throttle aging tail updates until we have a new tail that
@@ -420,24 +443,6 @@ static bool gen7_oa_buffer_check_unlocked(struct drm_i915_private *dev_priv)
                }
        }
 
-       /* Update the aged tail
-        *
-        * Flip the tail pointer available for read()s once the aging tail is
-        * old enough to trust that the corresponding data will be visible to
-        * the CPU...
-        */
-       if (aging_tail != INVALID_TAIL_PTR &&
-           ((now - dev_priv->perf.oa.oa_buffer.aging_timestamp) >
-            OA_TAIL_MARGIN_NSEC)) {
-               aged_idx ^= 1;
-               dev_priv->perf.oa.oa_buffer.aged_tail_idx = aged_idx;
-
-               aged_tail = aging_tail;
-
-               /* Mark that we need a new pointer to start aging... */
-               dev_priv->perf.oa.oa_buffer.tails[!aged_idx].offset = INVALID_TAIL_PTR;
-       }
-
        spin_unlock_irqrestore(&dev_priv->perf.oa.oa_buffer.ptr_lock, flags);
 
        return aged_tail == INVALID_TAIL_PTR ?