Horton

Re: Detection of hadware feature => please do not use signal

Tom Lane <tgl@sss.pgh.pa.us>

View thread View on postgr.es
From: Tom Lane <tgl@sss.pgh.pa.us>
To: Thomas Munro <thomas.munro@gmail.com>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>, Bastien Roucariès <rouca@debian.org>, pgsql-bugs@lists.postgresql.org
Date: 2024-11-23T01:39:55Z
Lists: pgsql-bugs

Attachments

Thomas Munro <thomas.munro@gmail.com> writes:
> Unfortunately it looks like NetBSD doesn't put AT_HWCAP into its
> auxv[], or even expose it to user space nicely, and those libraries
> don't seem to know of another way.  Hopefully NetBSD will align with
> those other systems for portability's sake.  The only other way I
> could find in a quick googling session is /usr/sbin/cpuctl, root only,
> no cigar (but a solid clue that the information is floating around
> somewhere, it just depends where exactly the root-only fencing is
> happening).

I poked into this with NetBSD and found that cpuctl's "identify"
option works just fine without root.  So that motivated me to dig
into its source code, and I end up with the attached.  Sadly it only
works in 64-bit; there is presumably a way to detect this in 32-bit
as well, but cpuctl doesn't know it.  That doesn't bother me a whole
lot though, at least not nearly as much as the 64-bit case.  Anybody
running PG on 32-bit ARM shouldn't be expecting great performance.

I've checked this on NetBSD 9.2 and 10.0.  I don't have hardware
that should return false (and there may not be any such 64-bit
hardware anyway...), so there's not much more I can test.

			regards, tom lane

Commits

  1. Update configure probes for CFLAGS needed for ARM CRC instructions.

  2. Support runtime CRC feature probing on NetBSD/ARM using sysctl().

  3. Use auxv to check for CRC32 instructions on ARM.

  4. Improve our method for probing the availability of ARM CRC instructions.