Horton

Re: Reduce timing overhead of EXPLAIN ANALYZE using rdtsc?

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: David Geier <geidav.pg@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Robert Haas <robertmhaas@gmail.com>, vignesh C <vignesh21@gmail.com>, Lukas Fittl <lukas@fittl.com>, Michael Paquier <michael@paquier.xyz>, Ibrar Ahmed <ibrar.ahmad@gmail.com>, Maciek Sakrejda <m.sakrejda@gmail.com>, pgsql-hackers@postgresql.org
Date: 2023-01-23T20:30:06Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. pg_test_timing: Also test RDTSC[P] timing, report time source, TSC frequency

  2. Allow retrieving x86 TSC frequency/flags from CPUID

  3. instrumentation: Standardize ticks to nanosecond conversion method

  4. instrumentation: Use Time-Stamp Counter on x86-64 to lower overhead

  5. Zero initialize uses of instr_time about to trigger compiler warnings

  6. instr_time: Represent time as an int64 on all platforms

  7. Add 250c8ee07ed to git-blame-ignore-revs

Hi,

On 2023-01-23 18:52:44 +0100, David Geier wrote:
> One thing I was wondering about: why did you chose to use a signed instead
> of an unsigned 64-bit integer for the ticks?

That's been the case since my first post in the thread :). Mainly, it seems
easier to detect underflow cases during subtraction that way. And the factor
of 2 in range doesn't change a whole lot.


> > > If you have time to look at the pg_test_timing part, it'd be
> > > appreciated. That's a it larger, and nobody looked at it yet. So I'm a bit
> > > hesitant to push it.
> > I haven't yet pushed the pg_test_timing (nor it's small prerequisite)
> > patch.
> > 
> > I've attached those two patches. Feel free to include them in your series if
> > you want, then the CF entry (and thus cfbot) makes sense again...
> I'll include them in my new patch set and also have a careful look at them.

Thanks.

Greetings,

Andres Freund