On Tue, Nov 28, 2023 at 7:51 AM Andres Freund <and...@anarazel.de> wrote: > > Hi, > > On 2023-11-25 14:09:14 +0700, John Naylor wrote: > > * Note: I have seen the threads with the idea of compiling multiple > > entire binaries, and switching at postmaster start. I think it's a > > good idea, but I also suspect detecting flags from the packager is an > > easier intermediate step. > > It's certainly an easier incremental step - but will it get us all that far?
Granted, not much. (TBH, I'm not sure how to design the multiple-binaries idea, but surely we're not the first project to think of this...) On Tue, Nov 28, 2023 at 4:21 AM Nathan Bossart <nathandboss...@gmail.com> wrote: > soon, but if we'd also like to start adding AVX2 enhancements (and I think > we will), I'm assuming we'll want to provide an easy way for users to > declare that they are building for v3+ CPUs. Yeah, I remember now I saw instruction selection change a single shift with -v3 which made the UTF-8 DFA significantly faster: https://www.postgresql.org/message-id/CAFBsxsHR08mHEf06PvrMRstfcyPJLwF69g0r1pvRrxWD4GEVoQ%40mail.gmail.com I imagine a number of places would get automatic improvements, and I think others have said the same thing. On Tue, Nov 28, 2023 at 5:26 AM Nathan Bossart <nathandboss...@gmail.com> wrote: > > I'm not sure why I thought checking each feature might be necessary. > > --with-isa-level could essentially just be an alias for adding all the > > CFLAGS for the extensions provided at that level, and --with-isa-level=auto > > would just mean -march=native. With those flags set, the ./configure > > checks would succeed with the base set of compiler flags passed in, which > > could be used as a heuristic for inlining (like CRC32C does today). > > Or, perhaps you mean removing those ./configure checks completely and > assuming that the compiler knows about the intrinsics required for the > specified ISA level... With the multiple-binaries, we might be able to assume, since it'll be opt-in (default is just use the baseline), but I'm not sure. And to avoid needing a newish compiler, than we could probably just use the equivalent, e.g. for -v2: -march=x86-64 -mmmx -msse -msse2 -mfxsr -msahf -mcx16 -mpopcnt -msse3 -msse4.1 -msse4.2 -mssse3 ...and it seems we'll want to make something up for Arm.
