From 6ebd85e10535dfaa9181842fe73834e51d4d3e6c 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.

PR-URL: https://github.com/joyent/node/pull/8789
Ref: https://github.com/strongloop/strong-agent/issues/3
Reviewed-by: Trevor Norris <trev.norris@gmail.com>
---
 src/platform-freebsd.cc | 5 -----
 src/platform-linux.cc   | 5 -----
 src/platform-macos.cc   | 5 -----
 src/platform-openbsd.cc | 5 -----
 src/platform-posix.cc   | 6 ++++++
 src/platform-solaris.cc | 5 -----
 tools/gyp/v8.gyp        | 2 +-
 7 files changed, 7 insertions(+), 26 deletions(-)

diff --git a/src/platform-freebsd.cc b/src/platform-freebsd.cc
index 511759c..5c90c6b 100644
--- a/src/platform-freebsd.cc
+++ b/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/src/platform-linux.cc b/src/platform-linux.cc
index beb2cce..3d6b304 100644
--- a/src/platform-linux.cc
+++ b/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/src/platform-macos.cc b/src/platform-macos.cc
index a216f6e..e54e3e4 100644
--- a/src/platform-macos.cc
+++ b/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/src/platform-openbsd.cc b/src/platform-openbsd.cc
index 408d4dc..72167de 100644
--- a/src/platform-openbsd.cc
+++ b/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/src/platform-posix.cc b/src/platform-posix.cc
index 5c3529d..8aecd56 100644
--- a/src/platform-posix.cc
+++ b/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/src/platform-solaris.cc b/src/platform-solaris.cc
index 07718fe..4e95ecc 100644
--- a/src/platform-solaris.cc
+++ b/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/tools/gyp/v8.gyp b/tools/gyp/v8.gyp
index 71cf366..c304925 100644
--- a/tools/gyp/v8.gyp
+++ b/tools/gyp/v8.gyp
@@ -715,7 +715,7 @@
             ['OS=="solaris"', {
                 'link_settings': {
                   'libraries': [
-                    '-lsocket -lnsl',
+                    '-lsocket -lnsl -lrt',
                 ]},
                 'sources': [
                   '../../src/platform-solaris.cc',