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Date: Mon, 30 May 2016 16:02:00 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>,
        Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>,
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        "Carlos O'Donell" <carlos@redhat.com>,
        Torvald Riegel <triegel@redhat.com>,
        Eric Dumazet <edumazet@google.com>
Subject: Re: [patch V2 2/7] futex: Hash private futexes per process
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On Mon, May 30, 2016 at 03:59:51PM +0200, Sebastian Andrzej Siewior wrote:
> 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?

I have no idea about the ticket stuff, i've not seen it. But yes, you
need to somehow guarantee no collisions.