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Commit 66747c18 authored by Steven Thomas's avatar Steven Thomas
Browse files

Fix BlockUntilVSync() to actually block 

In my refactoring in ag/2008740 I introduced a regression where blocking
until the next vsync would busy loop instead of actually blocking on an
event on the vsync fd. The problem was I changed the poll() call to
listen for POLLIN in addition to POLLPRI. While waiting for vsync events
we only want to listen for POLLPRI.

Bug: 36495351

Test: Confirmed with debug logs the busy loop bug and that we correctly
block with this patch applied.

Change-Id: Iec4951e014575a5d0ed3cfe3fc20ea91c67edf1b
parent e27fbca4

libs/vr/libvrflinger/hardware_composer.cpp

+9 −4
Original line number Diff line number Diff line
@@ -518,10 +518,13 @@ void HardwareComposer::SetDisplaySurfaces( 
    post_thread_cond_var_.notify_all();

}



int HardwareComposer::PostThreadPollInterruptible(int event_fd) {

int HardwareComposer::PostThreadPollInterruptible(int event_fd,

                                                  int requested_events) {

  pollfd pfd[2] = {

      {

          .fd = event_fd, .events = POLLPRI | POLLIN, .revents = 0,

          .fd = event_fd,

          .events = static_cast<short>(requested_events),

          .revents = 0,

      },

      {

          .fd = post_thread_interrupt_event_fd_.Get(),
@@ -645,7 +648,9 @@ int HardwareComposer::ReadVSyncTimestamp(int64_t* timestamp) { 
// TODO(eieio): This is pretty driver specific, this should be moved to a

// separate class eventually.

int HardwareComposer::BlockUntilVSync() {

  return PostThreadPollInterruptible(primary_display_vsync_event_fd_.Get());

  return PostThreadPollInterruptible(primary_display_vsync_event_fd_.Get(),

                                     // There will be a POLLPRI event on vsync

                                     POLLPRI);

}



// Waits for the next vsync and returns the timestamp of the vsync event. If
@@ -718,7 +723,7 @@ int HardwareComposer::SleepUntil(int64_t wakeup_timestamp) { 
    return -error;

  }



  return PostThreadPollInterruptible(timer_fd);

  return PostThreadPollInterruptible(timer_fd, POLLIN);

}



void HardwareComposer::PostThread() {

libs/vr/libvrflinger/hardware_composer.h

+1 −1
Original line number Diff line number Diff line
@@ -281,7 +281,7 @@ class HardwareComposer { 
  // Blocks until either event_fd becomes readable, or we're interrupted by a

  // control thread. Any errors are returned as negative errno values. If we're

  // interrupted, kPostThreadInterrupted will be returned.

  int PostThreadPollInterruptible(int event_fd);

  int PostThreadPollInterruptible(int event_fd, int requested_events);



  // BlockUntilVSync, WaitForVSync, and SleepUntil are all blocking calls made

  // on the post thread that can be interrupted by a control thread. If