Re: Optimize Arm64 crc32c implementation in Postgresql

Hi,

On 2018-04-03 19:05:19 +0300, Heikki Linnakangas wrote:
> On 01/04/18 20:32, Andres Freund wrote:
> > On 2018-03-06 02:44:35 +0800, Heikki Linnakangas wrote:
> > > * I tested this on Linux, with gcc and clang, on an ARM64 virtual machine
> > > that I had available (not an emulator, but a VM on a shared ARM64 server).
> >
> > Have you seen actual postgres performance benefits with the patch?
>
> I just ran a small test with pg_waldump, similar to what Abhijit Menon-Sen
> ran with the Slicing-by-8 and Intel SSE patches, when we added those
> (https://www.postgresql.org/message-id/20141119155811.GA32492%40toroid.org)
> I ran pgbench, with scale factor 5, until it had generated about 1 GB of
> WAL, and then I ran pg_waldump -z on that WAL. With slicing-by-8, it took
> about 7 s, and with the special CPU instructions, about 5 s. 'perf' showed
> that the CRC computation took about 30% of the CPU time before, and about
> 12% after, which sounds about right. That's not as big a speedup as we saw
> with the corresponding Intel SSE instructions back in 2014, but still quite
> worthwhile.

Cool. Based on a skim the patch looks reasonable. It's a bit sad that
it's effecively linux specific. But I'm not sure we can do anything
about that atm, given the state of the "discovery" APIs on various
platforms.

Greetings,

Andres Freund