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