linux-kernel - Re: [patch V2 2/7] futex: Hash private futexes per process

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Message-ID: <c36795eb-eeff-ea48-30cd-3333e121c7ee@linutronix.de>
Date:	Mon, 30 May 2016 15:59:51 +0200
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Sebastian Andrzej Siewior <sebastian@...akpoint.cc>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Darren Hart <darren@...art.com>,
	Ingo Molnar <mingo@...nel.org>,
	Michael Kerrisk <mtk.manpages@...glemail.com>,
	Davidlohr Bueso <dave@...olabs.net>, Chris Mason <clm@...com>,
	Carlos O'Donell <carlos@...hat.com>,
	Torvald Riegel <triegel@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: [patch V2 2/7] futex: Hash private futexes per process

On 05/30/2016 03:49 PM, Peter Zijlstra wrote:
>> The same thing can happen within a Task if you take my story from above
>> and replace task with thread. Completely understood.
> 
> Right; so I don't see the point of PREALLOCATE_HASH to cater for RT
> workloads if it still doesn't guarantee anything, esp. if the failure
> case is silent and obscure.

So what do you suggest? Adding trace points in order to learn about
possible collisions or using tickets (on top of this) to guarantee
being collision free?
Note: this as it, is already a win on NUMA boxes since the memory is
not referenced cross node.

Sebastian