From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S933674AbcIVOlg (ORCPT <rfc822;w@1wt.eu>);
        Thu, 22 Sep 2016 10:41:36 -0400
Received: from mx2.suse.de ([195.135.220.15]:40066 "EHLO mx2.suse.de"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1756646AbcIVOle (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Thu, 22 Sep 2016 10:41:34 -0400
Date: Thu, 22 Sep 2016 07:41:23 -0700
From: Davidlohr Bueso <dave@stgolabs.net>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>,
        Waiman Long <waiman.long@hpe.com>,
        Mike Galbraith <umgwanakikbuti@gmail.com>,
        Ingo Molnar <mingo@kernel.org>, Jonathan Corbet <corbet@lwn.net>,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        Jason Low <jason.low2@hpe.com>, Scott J Norton <scott.norton@hpe.com>,
        Douglas Hatch <doug.hatch@hpe.com>
Subject: Re: [RFC PATCH v2 3/5] futex: Throughput-optimized (TO) futexes
Message-ID: <20160922144123.GB13358@linux-80c1.suse>
References: <1474378963-15496-1-git-send-email-Waiman.Long@hpe.com>
 <1474378963-15496-4-git-send-email-Waiman.Long@hpe.com>
 <1474441172.27308.19.camel@gmail.com>
 <57E319BE.2050208@hpe.com>
 <20160922074932.GV5008@twins.programming.kicks-ass.net>
 <alpine.DEB.2.20.1609221236010.5599@nanos>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Disposition: inline
In-Reply-To: <alpine.DEB.2.20.1609221236010.5599@nanos>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Thu, 22 Sep 2016, Thomas Gleixner wrote:

>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?

Where would this leave the respective FUTEX_WAKE? A nop? Probably have to
differentiate the fact that the queue was empty, but there was a spinning,
instead of straightforward returning 0.

Thanks,
Davidlohr