Re: wrong query results on bf leafhopper
| От | Robins Tharakan |
|---|---|
| Тема | Re: wrong query results on bf leafhopper |
| Дата | |
| Msg-id | CAEP4nAwhtsZYFfzLGiq-tHJaEFw55TpnrKOxzMU1R+HsL3wjEg@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: wrong query results on bf leafhopper (David Rowley <dgrowleyml@gmail.com>) |
| Список | pgsql-hackers |
Hi,
On Thu, 29 May 2025 at 02:32, Andres Freund <andres@anarazel.de> wrote:
On 2025-05-28 22:51:14 +0930, Robins Tharakan wrote:
> Recently leafhopper failed again on the same test. For now I've paused it.
> To rule out the compiler (and its maturity on the architecture), I'll
> upgrade
> gcc (to nightly, or something more recent) and then re-enable to see if it
> changes anything.
+1 to a gcc upgrade, gcc 11 is rather old and out of upstream support.
Ack. I've updated leafhopper to gcc master. For now (to get the machine
green / running), I've disabled some flags, which I'll revisit in some time,
but hopefully that's not about compiler maturity - which is what I'm after here.
A kernel upgrade would be good too. My completely baseless gut feeling is that
some SIMD registers occassionally get corrupted, e.g. due to a kernel
interrupt / context switch not properly storing & restoring them. Weirdly
enought the instrumentation code is among the pieces of PG code most
vulnerable to that because we mostly don't do enough auto-vectorizable math,
but InstrEndLoop(), InstrStopNode() etc are trivially auto-vectorizable. I'm
pretty sure I've previously analyzed problems around this, but don't remember
the details (IA64 maybe?).
Fair point, I'll keep that option open. Originally, the machine was spun up to
evaluate the graviton4 ec2 instance and I'd like to explore whether the
stock-kernel / kernel-updates are able to keep the instance green (and resort
to updating the kernel only if I exhaust all other options - pg / compiler etc.).
-
robins
robins
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