On Fri, Sep 28, 2012 at 05:45:00PM +0200, Mike Hommey wrote: > On Fri, Sep 28, 2012 at 05:34:09PM +0200, Honza Bambas wrote: > > On 9/28/2012 12:58 PM, Mike Hommey wrote: > > >On Fri, Sep 28, 2012 at 06:45:24AM -0400, Benoit Jacob wrote: > > >>2012/9/28 Aryeh Gregor <a...@aryeh.name>: > > >>>On Thu, Sep 27, 2012 at 6:08 PM, Gregory Szorc <g...@mozilla.com> wrote: > > >>>>I actually held out on you with the initial landing of mach: there is > > >>>>more > > >>>>advanced tree building code in the pipes, complete with progress > > >>>>indicators. > > >>>>However, getting it reviewed is a challenge because we want the build > > >>>>system > > >>>>integration to be right. When that lands, mach will be smart enough to > > >>>>automatically define make flags optimal for your machine. e.g. -j == # > > >>>>of > > >>>>cores. So, you get optimal/parallel builds with no configuration > > >>>>necessary. > > >>>>This will all be configurable, of course. > > >>>Is -j equal to number of cores really optimal? I've always been told > > >>>that it's better to set it to more like twice the number of cores, > > >>>because some fraction of threads will normally be stalled on I/O and > > >>>you don't want cores idle. > > >>Depending on various factors, this can be offset by other factors like > > >>cores competing for limited resources such as CPU cache. On my core i7 > > >>with 8 logical cores and 8M cache and a SSD, -j8 is fastest. More > > >>generally while building a C++ project (C++ is computationally > > >>expensive to compile) you're not very likely to be IO bound, > > >>especially with a SSD. A C project might be different. > > >On my core i7, -j12 is fastest. bigger values are marginally slower > > >but they are all faster than -j8. > > > > > >Mike > > > > Win7 x64 / i7@3.9GHz / 8 cores / 12GB@1600MHz / SSD mirrored, warm > > clobbered build of debug desktop browser: > > -j12: 19m00s exactly > > -j9: 18m45s exactly > > > > Using more processes then cores is counter productive. I checked > > this 2 years ago already when build took just 13 minutes (we > > grow!!). > > Conclusion: YMMV, most likely, depending on OS ; I'm on Linux. IOW, it's > better to make it configurable.
And on OSX, the same is true http://blog.johnford.org/new-mac-builders-ssds-j-settings/ Mike _______________________________________________ dev-platform mailing list dev-platform@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-platform
