vp8: Remove sched_yield on POSIX systems

libvpx does sched_yield() on Linux. This is highly frowned upon these
days mainly because it is not needed and causes high scheduler overhead.

It is not needed because the kernel will preempt the task while it is
spinning which will imply a yield. On ChromeOS, not yielding has the
following improvements:

1. power_VideoCall test as seen on perf profile:

With yield:
     9.40%  [kernel]            [k] __pi___clean_dcache_area_poc
     7.32%  [kernel]            [k] _raw_spin_unlock_irq  <-- kernel scheduler

Without yield:
     8.76%  [kernel]            [k] __pi___clean_dcache_area_poc
     2.27%  [kernel]            [k] _raw_spin_unlock_irq  <-- kernel scheduler

As you can see, there is a 5% drop in the scheduler's CPU utilization.

2. power_VideoCall test results:

There is a 3% improvement on max video FPS, from 30 to 31. This
improvement is consistent.

Also note that the sched_yield() manpage itself says it is intended
only for RT tasks. From manpagE: "sched_yield() is intended for use
with real-time scheduling policies (i.e., SCHED_FIFO or SCHED_RR)
and very likely means your application design is broken."

BUG=b/168205004

Change-Id: Idb84ab19e94f6d0c7f9e544e7a407c946d5ced5c
Signed-off-by: Joel Fernandes <joelaf@google.com>

diff --git a/vp8/common/threading.h b/vp8/common/threading.h
index f9213693864e290afbe8c36c1ae6b62b22eb3761..1cfb9fec515461462a1160488284a87e22ed49b8 100644 (file)
--- a/vp8/common/threading.h
+++ b/vp8/common/threading.h
@@ -171,17 +171,20 @@ static inline int sem_destroy(sem_t *sem) {
 #define sem_wait(sem) (semaphore_wait(*sem))
 #define sem_post(sem) semaphore_signal(*sem)
 #define sem_destroy(sem) semaphore_destroy(mach_task_self(), *sem)
-#define thread_sleep(nms)
-/* { struct timespec ts;ts.tv_sec=0; ts.tv_nsec =
-   1000*nms;nanosleep(&ts, NULL);} */
 #else
 #include <unistd.h>
 #include <sched.h>
-#define thread_sleep(nms) sched_yield();
+#endif /* __APPLE__ */
+/* Not Windows. Assume pthreads */
+
+/* thread_sleep implementation: yield unless Linux/Unix. */
+#if defined(__unix__) || defined(__APPLE__)
+#define thread_sleep(nms)
 /* {struct timespec ts;ts.tv_sec=0;
     ts.tv_nsec = 1000*nms;nanosleep(&ts, NULL);} */
-#endif
-/* Not Windows. Assume pthreads */
+#else
+#define thread_sleep(nms) sched_yield();
+#endif /* __unix__ || __APPLE__ */
 
 #endif