commit ec7aa8a7287629522b4fab712bad465f0d132be4
author Ady Abraham <adyabr@google.com> Mon Jun 28 12:37:09 2021 -0700
committer Ady Abraham <adyabr@google.com> Mon Jun 28 12:38:41 2021 -0700
tree 059c8517ad2df5d50cdb58222606c0674f49b145
parent b3c68852626da31ae79870defbd54bfd9df7ffdf

SF: check previous present fence to avoid early presentation

If SurfaceFlinger finishes composition a vsyncPeriod or more before it
planned to, it sleeps before calling composer to present the frame to
avoid early presentation. In this CL we are removing the sleep if the
previous present fence is still pending, as early presentation is not
possible (composer has already a frame queued).

Bug: 190842189
Test: Bouncy ball while forcing client composition
Change-Id: Id913a21b3489973d82498c6154843656972b6e1a

services/surfaceflinger/DisplayHardware/HWComposer.cpp

diff --git a/services/surfaceflinger/DisplayHardware/HWComposer.cpp b/services/surfaceflinger/DisplayHardware/HWComposer.cpp
index 32f04e5..7e45dab 100644
--- a/services/surfaceflinger/DisplayHardware/HWComposer.cpp
+++ b/services/surfaceflinger/DisplayHardware/HWComposer.cpp
@@ -471,6 +471,7 @@
 status_t HWComposer::getDeviceCompositionChanges(
         HalDisplayId displayId, bool frameUsesClientComposition,
         std::chrono::steady_clock::time_point earliestPresentTime,
+        const std::shared_ptr<FenceTime>& previousPresentFence,
         std::optional<android::HWComposer::DeviceRequestedChanges>* outChanges) {
     ATRACE_CALL();
 
@@ -487,12 +488,16 @@
 
     hal::Error error = hal::Error::NONE;
 
-    // First try to skip validate altogether when we passed the earliest time
-    // to present and there is no client. Otherwise, we may present a frame too
-    // early or in case of client composition we first need to render the
+    // First try to skip validate altogether. We can do that when
+    // 1. The previous frame has not been presented yet or already passed the
+    // earliest time to present. Otherwise, we may present a frame too early.
+    // 2. There is no client composition. Otherwise, we first need to render the
     // client target buffer.
-    const bool canSkipValidate =
-            std::chrono::steady_clock::now() >= earliestPresentTime && !frameUsesClientComposition;
+    const bool prevFencePending =
+            previousPresentFence->getSignalTime() == Fence::SIGNAL_TIME_PENDING;
+    const bool canPresentEarly =
+            !prevFencePending && std::chrono::steady_clock::now() < earliestPresentTime;
+    const bool canSkipValidate = !canPresentEarly && !frameUsesClientComposition;
     displayData.validateWasSkipped = false;
     if (canSkipValidate) {
         sp<Fence> outPresentFence;
@@ -559,7 +564,8 @@
 }
 
 status_t HWComposer::presentAndGetReleaseFences(
-        HalDisplayId displayId, std::chrono::steady_clock::time_point earliestPresentTime) {
+        HalDisplayId displayId, std::chrono::steady_clock::time_point earliestPresentTime,
+        const std::shared_ptr<FenceTime>& previousPresentFence) {
     ATRACE_CALL();
 
     RETURN_IF_INVALID_DISPLAY(displayId, BAD_INDEX);
@@ -575,7 +581,9 @@
         return NO_ERROR;
     }
 
-    {
+    const bool previousFramePending =
+            previousPresentFence->getSignalTime() == Fence::SIGNAL_TIME_PENDING;
+    if (!previousFramePending) {
         ATRACE_NAME("wait for earliest present time");
         std::this_thread::sleep_until(earliestPresentTime);
     }