On Thu, Sep 24, 2020 at 10:28 PM YiFei Zhu <zhuyifei1999@xxxxxxxxx> wrote: > Ah. Makes sense. > > > Ironicailly, that's the only place I actually know for sure where people > > using x32 because it shows measurable (10%) speed-up for builders: > > https://lore.kernel.org/lkml/CAOesGMgu1i3p7XMZuCEtj63T-ST_jh+BfaHy-K6LhgqNriKHAA@xxxxxxxxxxxxxx > > Wow. 10% is significant. Makes you wonder why x32 hasn't conquered the world. > > > So, yes, as you and Jann both point out, it wouldn't be terrible to just > > ignore x32, it seems a shame to penalize it. That said, if the masking > > step from my v1 is actually noticable on a native workload, then yeah, > > probably x32 should be ignored. My instinct (not measured) is that it's > > faster than walking a small array.[citation needed] > > You convince me that penalizing supporting x32 would be a pity :( The > 10% is so nice I want it. I'm rethinking this -- the majority of our users will not use x32. I don't think it's that useful for the majority to run all the simulations and have the memory footprint if only a small minority will use it. I also just checked Debian, and it has boot-time disabling of the x32 arch downstream [1]: CONFIG_X86_X32=y CONFIG_X86_X32_DISABLED=y Which means we will still generate all the code for x32 in seccomp even though people probably won't be using it... I also talked to some of my peers and they had a point regarding how x32 limiting address space to 4GiB is very harsh on many modern language runtimes, so even though it provides a 10% speed boost, its adoption is hard -- one has to compile all the C libraries in x32 in addition to x86_64, since one would have programs needing > 4GiB address space needing x86_64 version of the libraries. [1] https://wiki.debian.org/X32Port YiFei Zhu
