Experimental pre-reading optimization to run on perf bots

Pre-reading chrome.dll prior to calling loadlibrary has shown significant
improvement int he startup performance. Temporarily enabling this for 
headless mode so that we can try out the effect on the perf bots.



Review URL: http://codereview.chromium.org/2814019

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@50386 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 57 insertions, 0 deletions

diff --git a/chrome/app/client_util.cc b/chrome/app/client_util.cc
index e4b2b78..4730e53 100644
--- a/chrome/app/client_util.cc
+++ b/chrome/app/client_util.cc
@@ -81,6 +81,10 @@ bool EnvQueryStr(const wchar_t* key_name, std::wstring* value) {
   return true;
 }
 
+bool IsRunningHeadless() {
+  return (0 != ::GetEnvironmentVariableW(L"CHROME_HEADLESS", NULL, 0));
+}
+
 // Expects that |dir| has a trailing backslash. |dir| is modified so it
 // contains the full path that was tried. Caller must check for the return
 // value not being null to dermine if this path contains a valid dll.
@@ -102,6 +106,59 @@ HMODULE LoadChromeWithDirectory(std::wstring* dir) {
 #else
   dir->append(installer_util::kChromeDll);
 #endif
+
+  // Experimental pre-reading optimization
+  // The idea is to pre read significant portion of chrome.dll in advance
+  // so that subsequent hard page faults are avoided.
+  DWORD pre_read_size_mb = 0;
+  const CommandLine& cmd_line = *CommandLine::ForCurrentProcess();
+  if (!cmd_line.HasSwitch(switches::kProcessType) &&
+      (IsRunningHeadless() || InstallUtil::IsChromeFrameProcess())) {
+    HKEY key = NULL;
+    if (::RegOpenKeyEx(HKEY_CURRENT_USER, L"Software\\Google\\ChromeFrame",
+                       0, KEY_QUERY_VALUE, &key) == ERROR_SUCCESS) {
+      DWORD unused = sizeof(pre_read_size_mb);
+      RegQueryValueEx(key, L"PreRead", NULL, NULL,
+                      reinterpret_cast<LPBYTE>(&pre_read_size_mb), &unused);
+      RegCloseKey(key);
+      key = NULL;
+    } else {
+      pre_read_size_mb = 16; // Read in first 16 MB by default.
+    }
+  }
+
+  if (pre_read_size_mb) {
+    HANDLE chrome_dll = CreateFile(dir->c_str(),
+                                       GENERIC_READ,
+                                       FILE_SHARE_READ | FILE_SHARE_WRITE,
+                                       NULL,
+                                       OPEN_EXISTING,
+                                       FILE_FLAG_SEQUENTIAL_SCAN,
+                                       NULL);
+    if (chrome_dll == INVALID_HANDLE_VALUE) {
+      DWORD error = GetLastError();
+      DLOG(ERROR) << __FUNCTION__ << " CreateFile( "
+          << dir->c_str() << " ) failed. Error: " << error;
+    } else {
+      const size_t kChunkSize = 1024 * 1024; // 1 MB
+      void* buffer = VirtualAlloc(NULL, kChunkSize, MEM_COMMIT, PAGE_READWRITE);
+      if (buffer) {
+        size_t read_size = pre_read_size_mb * kChunkSize;
+        DWORD read = 0;
+        while (::ReadFile(chrome_dll, buffer, kChunkSize, &read, NULL)) {
+          // nothing to do here...
+          read_size -= std::min(size_t(read), read_size);
+          if (!read || !read_size)
+            break;
+        }
+
+        VirtualFree(buffer, 0, MEM_RELEASE);
+      }
+
+      CloseHandle(chrome_dll);
+    }
+  }
+
   return ::LoadLibraryExW(dir->c_str(), NULL,
                           LOAD_WITH_ALTERED_SEARCH_PATH);
 }