ART: Tuning compiler thread count for application runtime

dex2oat decides the number of compiler threads to be spawned based
on the number of cores in the system. Using this max possible compiler
threads causes over parallelization on some platforms and there by
leads to longer install times. Reducing to fewer threads on these
platforms, improves this time by 60% to 100%.
Some APPs will call dex2oat at the first launch time(runtime). The
thread count tuning is needed for such scenario.

Change-Id: Id3a545f0300f93397627beeb697a7b7cfd912d52

dex2oat/Android.mk

@@ -21,6 +21,10 @@ include art/build/Android.executable.mk
 DEX2OAT_SRC_FILES := \
 	dex2oat.cc
 
+ifeq ($$(art_target_or_host),target)
+LOCAL_SHARED_LIBRARIES += libcutils
+endif
+
 # TODO: Remove this when the framework (installd) supports pushing the
 # right instruction-set parameter for the primary architecture.
 ifneq ($(filter ro.zygote=zygote64,$(PRODUCT_DEFAULT_PROPERTY_OVERRIDES)),)

dex2oat/dex2oat.cc

@@ -75,6 +75,9 @@
 #include "vector_output_stream.h"
 #include "well_known_classes.h"
 #include "zip_archive.h"
+#ifdef HAVE_ANDROID_OS
+#include "cutils/properties.h"
+#endif
 
 namespace art {
 
@@ -841,6 +844,18 @@ class Dex2Oat FINAL {
       }
     }
 
+    // Override the number of compiler threads with optimal value (thru system property)
+    #ifdef HAVE_ANDROID_OS
+    const char* propertyName = "ro.sys.fw.dex2oat_thread_count";
+    char thread_count_str[PROPERTY_VALUE_MAX];
+
+    if (property_get(propertyName, thread_count_str, "") > 0) {
+        if (ParseUint(thread_count_str, &thread_count_)) {
+            LOG(INFO) << "Adjusted thread count (for runtime dex2oat): " << thread_count_ << ", " << thread_count_str;
+        }
+    }
+    #endif
+
     image_ = (!image_filename_.empty());
     if (!requested_specific_compiler && !kUseOptimizingCompiler) {
       // If no specific compiler is requested, the current behavior is