Horton

Re: What is a typical precision of gettimeofday()?

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

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Hannu Krosing <hannuk@google.com>
Cc: Peter Eisentraut <peter@eisentraut.org>, "Andrey M. Borodin" <x4mmm@yandex-team.ru>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2024-07-02T18:33:41Z
Lists: pgsql-hackers

Commits

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  1. Force LC_NUMERIC to C while running TAP tests.

  2. Minor tweaks for pg_test_timing.

  3. Change pg_test_timing to measure in nanoseconds not microseconds.

Hannu Krosing <hannuk@google.com> writes:
> At least "does it run" tests should be there -

> For example with the current toolchain on MacOS I was able to compile
> __builtin_readcyclecounter(); but it crashed when the result was
> executed.

> The same code compiled *and run* fine on same laptop with Ubuntu 24.04

> We might also want to have some testing about available speedups from
> pg_bitmanip.h being used, but that could be tricky to test in an
> universal way.

Keep in mind that pg_test_timing is not just some random exercise in a
vacuum.  The point of it IMV is to provide data about the performance
one can expect from the instr_time.h infrastructure, which bears on
what kind of resolution EXPLAIN ANALYZE and other features have.  So
if we did want to depend on read_tsc() or __builtin_readcyclecounter()
or what-have-you, the way to go about it would be to change
instr_time.h to compile code that uses that.  I would consider that
to be a separate patch from what we're doing to pg_test_timing here.

			regards, tom lane