Update default DispSync offsets
Updates the default DispSync offsets to 1ms/1ms to avoid SurfaceFlinger
racing against hardware vsync on untuned video-mode panels, which can
result in a significant number of dropped frames. Also moves and
updates the documentation of the offsets, which used to live in
build/target/board/generic/BoardConfig.mk.
Bug: 30801895
Change-Id: I4cb09d840e2f16fb3d05df4d7abf58d9ba36f83b
diff --git a/services/surfaceflinger/Android.mk b/services/surfaceflinger/Android.mk
index dc5e97b..ffda035 100644
--- a/services/surfaceflinger/Android.mk
+++ b/services/surfaceflinger/Android.mk
@@ -79,18 +79,36 @@
LOCAL_CFLAGS += -DRUNNING_WITHOUT_SYNC_FRAMEWORK
endif
-# See build/target/board/generic/BoardConfig.mk for a description of this setting.
+# The following two BoardConfig variables define (respectively):
+#
+# - The phase offset between hardware vsync and when apps are woken up by the
+# Choreographer callback
+# - The phase offset between hardware vsync and when SurfaceFlinger wakes up
+# to consume input
+#
+# Their values can be tuned to trade off between display pipeline latency (both
+# overall latency and the lengths of the app --> SF and SF --> display phases)
+# and frame delivery jitter (which typically manifests as "jank" or "jerkiness"
+# while interacting with the device). The default values should produce a
+# relatively low amount of jitter at the expense of roughly two frames of
+# app --> display latency, and unless significant testing is performed to avoid
+# increased display jitter (both manual investigation using systrace [1] and
+# automated testing using dumpsys gfxinfo [2] are recommended), they should not
+# be modified.
+#
+# [1] https://developer.android.com/studio/profile/systrace.html
+# [2] https://developer.android.com/training/testing/performance.html
+
ifneq ($(VSYNC_EVENT_PHASE_OFFSET_NS),)
LOCAL_CFLAGS += -DVSYNC_EVENT_PHASE_OFFSET_NS=$(VSYNC_EVENT_PHASE_OFFSET_NS)
else
- LOCAL_CFLAGS += -DVSYNC_EVENT_PHASE_OFFSET_NS=0
+ LOCAL_CFLAGS += -DVSYNC_EVENT_PHASE_OFFSET_NS=1000000
endif
-# See build/target/board/generic/BoardConfig.mk for a description of this setting.
ifneq ($(SF_VSYNC_EVENT_PHASE_OFFSET_NS),)
LOCAL_CFLAGS += -DSF_VSYNC_EVENT_PHASE_OFFSET_NS=$(SF_VSYNC_EVENT_PHASE_OFFSET_NS)
else
- LOCAL_CFLAGS += -DSF_VSYNC_EVENT_PHASE_OFFSET_NS=0
+ LOCAL_CFLAGS += -DSF_VSYNC_EVENT_PHASE_OFFSET_NS=1000000
endif
ifneq ($(PRESENT_TIME_OFFSET_FROM_VSYNC_NS),)