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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Chris Mason <clm@meta.com>, linux-kernel@vger.kernel.org,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: futex performance regression from "futex: Allow automatic
 allocation of process wide futex hash"
Message-ID: <20250626135034.18sab4Xp@linutronix.de>
References: <3ad05298-351e-4d61-9972-ca45a0a50e33@meta.com>
 <20250604092815.UtG-oi0v@linutronix.de>
 <372d8277-7edb-4f78-99bd-6d23b8f94984@meta.com>
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 <aa6154d1-726c-4da1-a27b-69d2e8b449c6@meta.com>
 <20250606070638.2Wk45AMk@linutronix.de>
 <20250624190118.GB1490279@noisy.programming.kicks-ass.net>
 <71ea52f2-f6bf-4a55-84ba-d1442d13bc82@meta.com>
 <20250626131715.GI1613200@noisy.programming.kicks-ass.net>
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In-Reply-To: <20250626131715.GI1613200@noisy.programming.kicks-ass.net>

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.

Sebastian