From 48a85db19cf8ee66852871ee7bb7d869456a4485 Mon Sep 17 00:00:00 2001
From: Ben Noordhuis <info@bnoordhuis.nl>
Date: Thu, 27 Nov 2014 07:15:54 +0100
Subject: [PATCH] v8: don't busy loop in cpu profiler thread

Reduce the overhead of the CPU profiler by replacing sched_yield() with
nanosleep() in V8's tick event processor thread.  The former only yields
the CPU when there is another process scheduled on the same CPU.

Before this commit, the thread would effectively busy loop and consume
100% CPU time.  By forcing a one nanosecond sleep period rounded up to
the task scheduler's granularity (about 50 us on Linux), CPU usage for
the processor thread now hovers around 10-20% for a busy application.

Refs strongloop/strong-agent#3 and strongloop-internal/scrum-cs#37.
---
 deps/v8/src/platform-freebsd.cc | 5 -----
 deps/v8/src/platform-linux.cc   | 5 -----
 deps/v8/src/platform-macos.cc   | 5 -----
 deps/v8/src/platform-openbsd.cc | 5 -----
 deps/v8/src/platform-posix.cc   | 6 ++++++
 deps/v8/src/platform-solaris.cc | 5 -----
 deps/v8/tools/gyp/v8.gyp        | 2 +-
 7 files changed, 7 insertions(+), 26 deletions(-)

diff --git a/deps/v8/src/platform-freebsd.cc b/deps/v8/src/platform-freebsd.cc
index 511759c485e2..5c90c6bdae85 100644
--- a/deps/v8/src/platform-freebsd.cc
+++ b/deps/v8/src/platform-freebsd.cc
@@ -539,11 +539,6 @@ void Thread::SetThreadLocal(LocalStorageKey key, void* value) {
 }
 
 
-void Thread::YieldCPU() {
-  sched_yield();
-}
-
-
 class FreeBSDMutex : public Mutex {
  public:
   FreeBSDMutex() {
diff --git a/deps/v8/src/platform-linux.cc b/deps/v8/src/platform-linux.cc
index beb2ccee297f..3d6b3044e7bc 100644
--- a/deps/v8/src/platform-linux.cc
+++ b/deps/v8/src/platform-linux.cc
@@ -812,11 +812,6 @@ void Thread::SetThreadLocal(LocalStorageKey key, void* value) {
 }
 
 
-void Thread::YieldCPU() {
-  sched_yield();
-}
-
-
 class LinuxMutex : public Mutex {
  public:
   LinuxMutex() {
diff --git a/deps/v8/src/platform-macos.cc b/deps/v8/src/platform-macos.cc
index a216f6e4cacd..e54e3e4a4216 100644
--- a/deps/v8/src/platform-macos.cc
+++ b/deps/v8/src/platform-macos.cc
@@ -640,11 +640,6 @@ void Thread::SetThreadLocal(LocalStorageKey key, void* value) {
 }
 
 
-void Thread::YieldCPU() {
-  sched_yield();
-}
-
-
 class MacOSMutex : public Mutex {
  public:
   MacOSMutex() {
diff --git a/deps/v8/src/platform-openbsd.cc b/deps/v8/src/platform-openbsd.cc
index 408d4dc0f848..72167de9202d 100644
--- a/deps/v8/src/platform-openbsd.cc
+++ b/deps/v8/src/platform-openbsd.cc
@@ -593,11 +593,6 @@ void Thread::SetThreadLocal(LocalStorageKey key, void* value) {
 }
 
 
-void Thread::YieldCPU() {
-  sched_yield();
-}
-
-
 class OpenBSDMutex : public Mutex {
  public:
   OpenBSDMutex() {
diff --git a/deps/v8/src/platform-posix.cc b/deps/v8/src/platform-posix.cc
index 5c3529d4458c..8aecd560e908 100644
--- a/deps/v8/src/platform-posix.cc
+++ b/deps/v8/src/platform-posix.cc
@@ -392,6 +392,12 @@ void OS::StrNCpy(Vector<char> dest, const char* src, size_t n) {
 }
 
 
+void Thread::YieldCPU() {
+  const timespec delay = { 0, 1 };
+  nanosleep(&delay, NULL);
+}
+
+
 // ----------------------------------------------------------------------------
 // POSIX socket support.
 //
diff --git a/deps/v8/src/platform-solaris.cc b/deps/v8/src/platform-solaris.cc
index 07718fe50b99..4e95ecc6a48b 100644
--- a/deps/v8/src/platform-solaris.cc
+++ b/deps/v8/src/platform-solaris.cc
@@ -527,11 +527,6 @@ void Thread::SetThreadLocal(LocalStorageKey key, void* value) {
 }
 
 
-void Thread::YieldCPU() {
-  sched_yield();
-}
-
-
 class SolarisMutex : public Mutex {
  public:
   SolarisMutex() {
diff --git a/deps/v8/tools/gyp/v8.gyp b/deps/v8/tools/gyp/v8.gyp
index 71cf36649ada..c304925908ac 100644
--- a/deps/v8/tools/gyp/v8.gyp
+++ b/deps/v8/tools/gyp/v8.gyp
@@ -715,7 +715,7 @@
             ['OS=="solaris"', {
                 'link_settings': {
                   'libraries': [
-                    '-lsocket -lnsl',
+                    '-lsocket -lnsl -lrt',
                 ]},
                 'sources': [
                   '../../src/platform-solaris.cc',