linux-kernel - Re: [RFC PATCH v2 3/5] futex: Throughput-optimized (TO) futexes

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Date:   Thu, 22 Sep 2016 15:34:06 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     Waiman Long <waiman.long@....com>,
        Mike Galbraith <umgwanakikbuti@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, Davidlohr Bueso <dave@...olabs.net>,
        Jason Low <jason.low2@....com>,
        Scott J Norton <scott.norton@....com>,
        Douglas Hatch <doug.hatch@....com>
Subject: Re: [RFC PATCH v2 3/5] futex: Throughput-optimized (TO) futexes

On Thu, 22 Sep 2016, Peter Zijlstra wrote:
> On Wed, Sep 21, 2016 at 07:37:34PM -0400, Waiman Long wrote:
> > On 09/21/2016 02:59 AM, Mike Galbraith wrote:
> > >On Tue, 2016-09-20 at 09:42 -0400, Waiman Long wrote:
> > >>This patch introduces a new futex implementation called
> > >>throughput-optimized (TO) futexes.
> > >nit: 'TO' sounds way too much like timeout... TP?  You even use 'to' as
> > >shorthand for timeout in the next patch.
> > 
> > I agree. I am not that satisfied with the TO name. So I will change it to TP
> > in my next revision of the patch. Thanks for the suggestion.
> 
> I'd leave out the TO part entirely (or only mention it in changelogs).
> 
> That is, I'd call the futex ops: FUTEX_LOCK and FUTEX_UNLOCK.

That brings me to a different question:

How is user space going to support this, i.e. is this some extra magic for
code which implements its own locking primitives or is there going to be a
wide use via e.g. glibc.

Also what's the reason that we can't do probabilistic spinning for
FUTEX_WAIT and have to add yet another specialized variant of futexes?

Thanks,

	tglx