Re: postmaster uses more CPU in 18 beta1 with io_method=io_uring

Hi Andres / Robert,

On Mon, Sep 8, 2025 at 5:55 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> Hi,
>
> On 2025-09-06 09:12:19 -0400, Robert Treat wrote:
[..]
> > > [..], but 6.1 is the LTS kernel, so plenty of people
> > > are going to hit those regressions with io_uring io_method, won't
> > > they?
>
> I doubt it, but who knows.

RHEL 8.x won't have it (RH KB [1] says "RHEL 8.x: The addition to
RHEL8 was being tracked in private Bug 1881561 - Add io_uring support.
Unfortunately, it has been decided that io_uring support will not be
enabled in RHEL8."

RHEL 9.x seems to be all based on 5.14.x (so much below 6.5.x) and
states that uring is in Tech Preview there and is disabled, but it can
be enabled via sysctl. Hard to tell what they will backpatch into
5.14.x there. So if anywhere, I would speculate it would be RHEL9 (?),
therefore 5.14.x (+their custom back patches).

> > > I can try to prepare a patch, please just let me know.
>
> Yes, please do.

Attached.

> If they just upgrade in-place, they won't use io_uring. And they won't simply
> use io_uring with this large max_connections without also tuning the file
> descriptor limits...

Business as usual, just another obstacle...

-J.