On Saturday, March 04, 2017 11:16:11 PM Konstantin Belousov wrote: > On Sat, Mar 04, 2017 at 03:49:52PM -0500, Pedro Giffuni wrote: > > The number came out from an old posting involving buildworld times, which I > > can???t find now :(. > > Things seem to have changed a lot: it was surely using GCC back then, I > > don???t believe clang does much distinction about 486 at all. > > > > BTW, does it make sense to keep i586 in the configuration still? Both i486 > > and i586 were once removed but later re-instated in r205336. > > > What did make significant impact on 32bit shared libraries some time ago > was to compile them with -mtune=i686. Default PIC prologue effectively > neutered return stack predictor, adding uneccessary overhead to already > expensive PIC code. I think that this is even measureable, i.e. it might > give >= 5% of difference. > > I did not rechecked modern compilers WRT the generated PIC code, but I doubt > that the thing changed recently. > > Several notes: -mtune is not -march, i.e. the code would be still targeted > for 486 instruction set, but scheduling is optimized for more modern CPUs. > Also, recent gcc puts specific meaning into -mtune=i686, interpreting it > as request for scheduling for generic modern CPUs. We already compile > 32bit compat libs on amd64 with -march=i686. > > Working on this stuff would be much more useful than tweaking kernel config > for CPU detection.
Hmm, I originally wanted to use -mtune=i686 (spelled as -mcpu=pentiumpro) on i386 builds for this reason, but I removed it at bde@'s request in r125252. I would be happy to go back to adding -mtune for i386 when CPUTYPE isn't specified. -- John Baldwin _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
