On Sat, Sep 24, 2016 at 10:52 AM, Markus Trippelsdorf <mar...@trippelsdorf.de> wrote: > On 2016.09.23 at 15:29 +0200, Richard Biener wrote: >> > >> > So 50000 looks too big to me. >> >> I think the issue is that the default number of partitions is too high >> (32) which pessimizes 4-core machines if the units are too small. > > The more partitions are used the less memory is required at LTRANS time. > > If for example you limit partitions to 4 on a 4-core machine with 8GB > memory, you would start swapping when building Firefox. > > And even lto-partitions=8 is slower than the default of 32: > > (Firefox libxul build times with gcc-6.) > > --param=lto-partitions=8 -flto=4: > 1670.19s user 23.39s system 305% cpu 9:14.13 total > > default -flto=4: > 1668.94s user 32.51s system 320% cpu 8:50.36 total > > If someone wants fewer partitions he can use -flto-partition=one/none > or --param=lto-partitions=1.
I know all this. But then we seem to be stuck at 32 partitions from an input size of 32 * lto-partition-min up to 32 * lto-partition-max which is currently two orders of magnitude of difference in input size! That can't be a good heuristic. It's also about temporary disk space of which we use more the more partitions we use (because we essentially duplicate the whole global types/decls section for each partition). I'm not saying increasing lto-partition-min is the best solution but it certainly looks like the most appealing one to me. Richard. > -- > Markus
