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. Mike _______________________________________________ dev-platform mailing list dev-platform@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-platform
