On Tue, 2020-08-25 at 10:17 +0100, Daniel P. Berrangé wrote: > On Sat, Aug 22, 2020 at 12:53:24PM +0200, Germano Massullo wrote: > > I think soon we will have a big boost in Koji performances thanks to > > Giuliano Belinassi and his work on addressing GCC parallelization > > bottlenecks. According to Phoronix, compiling individual files in > > parallel may have up to ~1.9x speedup: > > https://www.phoronix.com/scan.php?page=news_item&px=GCC-fparallel-jobs-Patches > > AFAICT, that is referring to parallelizing single file compilation to > make use of multiple cores. That's only useful if the other cores on > your host are otherwise idle. Correct. It's going to be most helpful when there's a large TU with many functions and there's nothing else going on to keep the cores/threads busy. > > In koji we use parallel make (or equivalent) so that multiple files > are compiled in parallel. Thus most of the time all cores will be fully > utilized. RIght. Except for those which override the parallel make flags because they're missing dependencies. But these are very much the exception, not the rule. > IOW, don't get too excited by the x1.9 speedup claim. I doubt we'll > see that in kojki except in niche scenarios where a project's build > is bottlenecked by a serialization point on compiling one file. Right. Also note the code isn't accepted upstream yet. I strongly suspect there's going to be more work required to make what Guiuliano's work ready for prime time. On a positive note, my understanding from talking to Giuliano last year was that he was trying to parallelize GCC itself which I thought was untractable for a student project given the amount of unprotected global state. Instead I think he ended up using the LTO partitioning code to find TU split points, then feeds those into distinct fork/exec'd copies of GCC which is a much simpler problem to solve. So there may be uses for his work. Obviously the GCC team will continue to monitor and if/when we think there's a change we should make for Fedora to exploit Giuliano's work we'll propose it. jeff > _______________________________________________ devel mailing list -- devel@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxxxxxxxx Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/devel@xxxxxxxxxxxxxxxxxxxxxxx
