cr: Allow ninja to use more CPUs on many core workstations.

Before this patch, the number of CPUs allowed to be used by ninja was hardcoded.
This patch tries to find the optimal number by querying the number of available
cpus in the system.

BUG=324806
NOTRY=true

Review URL: https://codereview.chromium.org/248673002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@266118 0039d316-1c4b-4281-b951-d872f2087c98

tools/cr/cr/actions/ninja.py

@@ -4,6 +4,7 @@
 
 """A module to add ninja support to cr."""
 
+import multiprocessing
 import os
 
 import cr
@@ -20,10 +21,11 @@ class NinjaBuilder(cr.Builder):
   """An implementation of Builder that uses ninja to do the actual build."""
 
   # Some basic configuration installed if we are enabled.
+  EXTRA_FOR_IO_BOUND_JOBS = 2
   ENABLED = cr.Config.From(
       NINJA_BINARY=os.path.join('{DEPOT_TOOLS}', 'ninja'),
-      NINJA_JOBS=10,
-      NINJA_PROCESSORS=4,
+      NINJA_JOBS=multiprocessing.cpu_count() + EXTRA_FOR_IO_BOUND_JOBS,
+      NINJA_PROCESSORS=multiprocessing.cpu_count(),
       NINJA_BUILD_FILE=os.path.join('{CR_BUILD_DIR}', 'build.ninja'),
       # Don't rename to GOMA_* or Goma will complain: "unkown GOMA_ parameter".
       NINJA_GOMA_LINE='cc = {CR_GOMA_CC} $',
@@ -35,8 +37,7 @@ class NinjaBuilder(cr.Builder):
       GOMA_DIR='{CR_GOMA_DIR}',
       GYP_DEF_gomadir='{CR_GOMA_DIR}',
       GYP_DEF_use_goma=1,
-      NINJA_JOBS=200,
-      NINJA_PROCESSORS=12,
+      NINJA_JOBS=multiprocessing.cpu_count() * 10,
   )
   # A placeholder for the system detected configuration
   DETECTED = cr.Config('DETECTED')