MIME-Version: 1.0
References: <3bdce15d-25ec-4c49-9906-818803462897@gmail.com>
 <CAP53PkyooCeR8YV0BUD_xC7oTZESHz8OdA=tP7pBRHFVQ9xtKg@mail.gmail.com>
 <CAP53PkxaDpPCbXeA=OpmY4DUxBVHzgivXzpA62_tRE62xfc9nA@mail.gmail.com>
 <CAKZiRmzF50+drGgm6F-K1dQnuT=Khob0Q_dfZdv0-1iq4TVa4Q@mail.gmail.com>
 <vbfdgjxn4rqwbnznks4zstx7t34dcrhubbmse775ou4nmcjqzi@4rugaq7sftac>
 <1e0462f0-8274-4d57-aa39-9b6ebeb954da@gmail.com> <CAP53PkxAtD_ArzxaXPMgAKTfT5Da34o-oN9JY32UbhFS3U=-6A@mail.gmail.com>
 <aY5Si7r2SMe4fRPc@alap3.anarazel.de> <CAP53PkxNJ2Y6G8PEpQn1zKa6ODE6k1-oP9DNqWjkTj=dC8_KiA@mail.gmail.com>
 <41528b05-62be-4a5a-abd8-2af2dd84a1be@gmail.com> <r5snevsnkyoifjqldu6gcssbnrnezpplq4ofcmekjfvzzu32dc@5rn26itd4ubr>
 <CAP53Pkx1bK1FB71_nBqYmzvSSXnp_MbE0ZDnU+baPJF6Ud2WDA@mail.gmail.com>
In-Reply-To: <CAP53Pkx1bK1FB71_nBqYmzvSSXnp_MbE0ZDnU+baPJF6Ud2WDA@mail.gmail.com>
From: Jakub Wartak <jakub.wartak@enterprisedb.com>
Date: Wed, 25 Feb 2026 12:57:19 +0100
Message-ID: <CAKZiRmwWKBzLmCjiENVOS8FijDsoOyCh29YwSiZcak61oM77DA@mail.gmail.com>
Subject: Re: Reduce timing overhead of EXPLAIN ANALYZE using rdtsc?
To: Lukas Fittl <lukas@fittl.com>
Cc: Andres Freund <andres@anarazel.de>, Hannu Krosing <hannuk@google.com>, 
	Robert Haas <robertmhaas@gmail.com>, Pavel Stehule <pavel.stehule@gmail.com>, 
	vignesh C <vignesh21@gmail.com>, Michael Paquier <michael@paquier.xyz>, 
	Ibrar Ahmed <ibrar.ahmad@gmail.com>, Maciek Sakrejda <m.sakrejda@gmail.com>, 
	pgsql-hackers <pgsql-hackers@postgresql.org>, David Geier <geidav.pg@gmail.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Archived-At: <https://www.postgresql.org/message-id/CAKZiRmwWKBzLmCjiENVOS8FijDsoOyCh29YwSiZcak61oM77DA%40mail.gmail.com>
Precedence: bulk

On Wed, Feb 25, 2026 at 11:01=E2=80=AFAM Lukas Fittl <lukas@fittl.com> wrot=
e:
[..]
> 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 ou=
t
that set_tsc_frequency_khz() returns false and tsc_frequency_khz=3D=3D0 bef=
ore 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 w=
ay of
informing users why he cannot SET timing_clock_source to TSC. Possibly errh=
int()
could differentiate the reason? E.g.
  "failed to auto-detect TSC frequency (potential hypervisor issue)" or
  "CPU RDTSCP instructions are not available"

-J.