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

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Message-ID: <20250627121441.LpTsB5q5@linutronix.de>
Date: Fri, 27 Jun 2025 14:14:41 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Chris Mason <clm@...a.com>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: futex performance regression from "futex: Allow automatic
 allocation of process wide futex hash"

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