From 43118373ed5f299ef1595c8bf4b0540f4e89f2e6 Mon Sep 17 00:00:00 2001
From: Ryan Hunt <rhunt@eqrion.net>
Date: Thu, 25 Jan 2018 14:12:39 -0600
Subject: [PATCH] Enable parallel painting on OSX and cap the amount of paint
 workers to 4. (bug 1430793, r=milan)

--HG--
extra : rebase_source : 9d5c853f84b160819540cc062fb84f4bea8fcb02
---
 gfx/layers/PaintThread.cpp  | 9 +++------
 modules/libpref/init/all.js | 6 +++++-
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/gfx/layers/PaintThread.cpp b/gfx/layers/PaintThread.cpp
index 0a72f8f3c666..a92441cd3409 100644
--- a/gfx/layers/PaintThread.cpp
+++ b/gfx/layers/PaintThread.cpp
@@ -137,13 +137,10 @@ PaintThread::CalculatePaintWorkerCount()
 
   int32_t workerCount = gfxPrefs::LayersOMTPPaintWorkers();
 
-  // If not manually specified, default to (cpuCores * 3) / 4
+  // If not manually specified, default to (cpuCores * 3) / 4, and clamp
+  // between 1 and 4. If a user wants more, they can manually specify it
   if (workerCount < 1) {
-    workerCount = std::max((cpuCores * 3) / 4, 1);
-
-    if (workerCount > 32) {
-      workerCount = 32;
-    }
+    workerCount = std::min(std::max((cpuCores * 3) / 4, 1), 4);
   }
 
   return workerCount;
diff --git a/modules/libpref/init/all.js b/modules/libpref/init/all.js
index a988a29397c9..386ce7070073 100644
--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -5935,5 +5935,9 @@ pref("layers.omtp.enabled", true);
 #else
 pref("layers.omtp.enabled", false);
 #endif
-pref("layers.omtp.release-capture-on-main-thread", false);
+#if defined(XP_MACOSX)
+pref("layers.omtp.paint-workers", -1);
+#else
 pref("layers.omtp.paint-workers", 1);
+#endif
+pref("layers.omtp.release-capture-on-main-thread", false);