linux-kernel - Re: [PATCH-tip v5 17/21] TP-futex: Group readers together in wait queue

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Message-ID: <13281.1486146235@turing-police.cc.vt.edu>
Date:   Fri, 03 Feb 2017 13:23:55 -0500
From:   valdis.kletnieks@...edu
To:     Waiman Long <longman@...hat.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Mike Galbraith <umgwanakikbuti@...il.com>,
        Scott J Norton <scott.norton@....com>
Subject: Re: [PATCH-tip v5 17/21] TP-futex: Group readers together in wait queue

On Fri, 03 Feb 2017 13:03:50 -0500, Waiman Long said:

> On a 2-socket 36-core E5-2699 v3 system (HT off) running on a 4.10

>                           WW futex       TP futex         Glibc
>                           --------       --------         -----
> Total locking ops        35,707,234     58,645,434     10,930,422
> Per-thread avg/sec           99,149        162,887         30,362
> Per-thread min/sec           93,190         38,641         29,872
> Per-thread max/sec          104,213        225,983         30,708

Do we understand where the 38K number came from?  I'm a bit concerned that the
min-to-max has such a large dispersion compared to all the other numbers.  Was
that a worst-case issue, and is the worst-case something likely to happen in
production, or requires special effort to trigger?


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