Re: futex performance regression from "futex: Allow automatic allocation of process wide futex hash"

From: Sebastian Andrzej Siewior
Date: Fri Jun 27 2025 - 08:15:52 EST


On 2025-06-27 13:04:57 [+0200], Peter Zijlstra wrote:
> On Thu, Jun 26, 2025 at 03:50:34PM +0200, Sebastian Andrzej Siewior wrote:
> > On 2025-06-26 15:17:15 [+0200], Peter Zijlstra wrote:
> > > > I'd vote for defaulting to global for one more release.
> > >
> > > Probably best to do that; means we don't have to rush crazy code :-)
> >
> > If we do that, that means we need to ensure that the private hash is not
> > deployed while a thread is created and the prctl() function can only
> > work create the private hash if the application is single threaded.
>
> I was thinking something like so..

Okay. That increases the motivation to fix it in one cycle.
Anything you want me to do here?

Sebastian