| From: | Jakub Wartak <jakub(dot)wartak(at)enterprisedb(dot)com> |
|---|---|
| To: | Lukas Fittl <lukas(at)fittl(dot)com> |
| Cc: | Andres Freund <andres(at)anarazel(dot)de>, Hannu Krosing <hannuk(at)google(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, vignesh C <vignesh21(at)gmail(dot)com>, Michael Paquier <michael(at)paquier(dot)xyz>, Ibrar Ahmed <ibrar(dot)ahmad(at)gmail(dot)com>, Maciek Sakrejda <m(dot)sakrejda(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, David Geier <geidav(dot)pg(at)gmail(dot)com> |
| Subject: | Re: Reduce timing overhead of EXPLAIN ANALYZE using rdtsc? |
| Date: | 2026-02-25 11:57:19 |
| Message-ID: | CAKZiRmwWKBzLmCjiENVOS8FijDsoOyCh29YwSiZcak61oM77DA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, Feb 25, 2026 at 11:01 AM Lukas Fittl <lukas(at)fittl(dot)com> wrote:
[..]
> See attached v9, rebased, with feedback addressed, unless otherwise noted.
FWIW, I've tried this on FreeBSD and I couldn't understand why I
couldn't enable TSC
(atlought) the cpuid tools reported RDTSCP being available. I have found out
that set_tsc_frequency_khz() returns false and tsc_frequency_khz==0 before even
inquiry for is_rdtscp_available() is done. As this was on virtualbox VM (so not
suppoprted by current code), I think this is pretty clear we'll need some way of
informing users why he cannot SET timing_clock_source to TSC. Possibly errhint()
could differentiate the reason? E.g.
"failed to auto-detect TSC frequency (potential hypervisor issue)" or
"CPU RDTSCP instructions are not available"
-J.
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