Merge lp:~dandrader/mir/cross-compile-parallel into lp:mir

[Daniel d'Andrada]

Make cross-compile-chroot.sh build in parallel when suitable

Use all available CPU cores to speed up the build

[Daniel van Vugt (vanvugt)]

Good idea but:
NUM_JOBS=$(( `grep -c ^processor /proc/cpuinfo` + 1 ))

Why the "+ 1"?

review: Needs Information

[Daniel d'Andrada (dandrader)]

> Good idea but:
> NUM_JOBS=$(( `grep -c ^processor /proc/cpuinfo` + 1 ))
>
> Why the "+ 1"?

To squeeze more juice out of the CPU, helping ensure it's 100% busy building the code. :)
In my experience a CPU can handle more build threads than its number of cores without hampering the execution speed of the individual threads.

[Alan Griffiths (alan-griffiths)]

> > Good idea but:
> > NUM_JOBS=$(( `grep -c ^processor /proc/cpuinfo` + 1 ))
> >
> > Why the "+ 1"?
>
> To squeeze more juice out of the CPU, helping ensure it's 100% busy building
> the code. :)
> In my experience a CPU can handle more build threads than its number of cores
> without hampering the execution speed of the individual threads.

I sort of agree - compilation (even C++) is usually I/O bound.

I think "+ 1" is a bit arbitrary, but not harmful.

review: Approve

[PS Jenkins bot (ps-jenkins)]

PASSED: Continuous integration, rev:1098
http://jenkins.qa.ubuntu.com/job/mir-team-mir-development-branch-ci/71/
Executed test runs:
    SUCCESS: http://jenkins.qa.ubuntu.com/job/mir-android-saucy-i386-build/2199
    SUCCESS: http://jenkins.qa.ubuntu.com/job/mir-clang-saucy-amd64-build/2084
    SUCCESS: http://jenkins.qa.ubuntu.com/job/mir-team-mir-development-branch-saucy-amd64-ci/71
        deb: http://jenkins.qa.ubuntu.com/job/mir-team-mir-development-branch-saucy-amd64-ci/71/artifact/work/output/*zip*/output.zip

Click here to trigger a rebuild:
http://s-jenkins:8080/job/mir-team-mir-development-branch-ci/71/rebuild

review: Approve (continuous-integration)

=== modified file 'cross-compile-chroot.sh'
--- cross-compile-chroot.sh	2013-08-28 03:41:48 +0000
+++ cross-compile-chroot.sh	2013-10-02 10:13:22 +0000
@@ -4,6 +4,7 @@
 set -e
 
 BUILD_DIR=build-android-arm
+NUM_JOBS=$(( `grep -c ^processor /proc/cpuinfo` + 1 ))
 
 if [ "$MIR_NDK_PATH" = "" ]; then
     export MIR_NDK_PATH=`pwd`/partial-armhf-chroot
@@ -32,6 +33,6 @@
       -DMIR_PLATFORM=android \
       .. 
 
-    cmake --build .
+    cmake --build . -- -j${NUM_JOBS}
 
 popd ${BUILD_DIR} > /dev/null