From: Avi Kivity <avi@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Darren Hart <dvhltc@us.ibm.com>,
linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
Eric Dumazet <eric.dumazet@gmail.com>,
"Peter W. Morreale" <pmorreale@novell.com>,
Rik van Riel <riel@redhat.com>,
Steven Rostedt <rostedt@goodmis.org>,
Gregory Haskins <ghaskins@novell.com>,
Sven-Thorsten Dietrich <sdietrich@novell.com>,
Chris Mason <chris.mason@oracle.com>,
John Cooper <john.cooper@third-harmonic.com>,
Chris Wright <chrisw@sous-sol.org>
Subject: Re: [PATCH V2 0/6][RFC] futex: FUTEX_LOCK with optional adaptive spinning
Date: Tue, 06 Apr 2010 19:10:23 +0300 [thread overview]
Message-ID: <4BBB5CEF.6060803@redhat.com> (raw)
In-Reply-To: <1270562948.1595.442.camel@laptop>
On 04/06/2010 05:09 PM, Peter Zijlstra wrote:
> On Tue, 2010-04-06 at 16:41 +0300, Avi Kivity wrote:
>
>> On 04/06/2010 04:35 PM, Peter Zijlstra wrote:
>>
>>> On Tue, 2010-04-06 at 16:28 +0300, Avi Kivity wrote:
>>>
>>>
>>>> Yes, but that's the best case for spinning. You could simply use a
>>>> userspace spinlock in this case.
>>>>
>>>>
>>> Userspace spinlocks are evil.. they should _never_ be used.
>>>
>>>
>> But in this case they're fastest. If we don't provide a non-evil
>> alternative, people will use them.
>>
>>
> That's what FUTEX_LOCK is about.
>
That works for the uncontended case. For the contended case, the waiter
and the owner have to go into the kernel and back out to transfer
ownership. In the non-adaptive case you have to switch to the idle task
and back as well, and send an IPI. That's a lot of latency if the
unlock happened just after the waiter started the descent into the kernel.
--
error compiling committee.c: too many arguments to function
next prev parent reply other threads:[~2010-04-06 16:11 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-04-05 20:23 [PATCH V2 0/6][RFC] futex: FUTEX_LOCK with optional adaptive spinning Darren Hart
2010-04-05 20:23 ` [PATCH 1/6] futex: replace fshared and clockrt with combined flags Darren Hart
2010-04-05 20:23 ` [PATCH 2/6] futex: add futex_q static initializer Darren Hart
2010-04-05 20:23 ` [PATCH 3/6] futex: refactor futex_lock_pi_atomic Darren Hart
2010-04-05 20:23 ` [PATCH 4/6] futex: Add FUTEX_LOCK with optional adaptive spinning Darren Hart
2010-04-06 16:55 ` Thomas Gleixner
2010-04-07 17:26 ` Darren Hart
2010-04-07 19:59 ` Thomas Gleixner
2010-04-08 3:25 ` Darren Hart
2010-04-08 23:10 ` Peter W. Morreale
2010-04-09 5:41 ` Darren Hart
2010-04-09 13:13 ` Peter W. Morreale
2010-04-05 20:23 ` [PATCH 5/6] futex: handle timeout inside adaptive lock spin Darren Hart
2010-04-06 8:27 ` Thomas Gleixner
2010-04-07 17:31 ` Darren Hart
2010-04-07 18:44 ` Gregory Haskins
2010-04-07 23:15 ` Darren Hart
2010-04-05 20:23 ` [PATCH 6/6] futex: Add aggressive adaptive spinning argument to FUTEX_LOCK Darren Hart
2010-04-08 5:58 ` Darren Hart
2010-04-05 20:48 ` [PATCH V2^W V4 0/6][RFC] futex: FUTEX_LOCK with optional adaptive spinning Darren Hart
2010-04-05 21:15 ` [PATCH V2 " Avi Kivity
2010-04-05 21:54 ` Darren Hart
2010-04-05 22:21 ` Avi Kivity
2010-04-05 22:59 ` Darren Hart
2010-04-06 13:28 ` Avi Kivity
2010-04-06 13:35 ` Peter Zijlstra
2010-04-06 13:41 ` Avi Kivity
2010-04-06 14:09 ` Peter Zijlstra
2010-04-06 16:10 ` Avi Kivity [this message]
2010-04-06 16:53 ` Alan Cox
2010-04-06 13:51 ` Alan Cox
2010-04-06 15:28 ` Darren Hart
2010-04-06 16:06 ` Avi Kivity
2010-04-06 16:14 ` Thomas Gleixner
2010-04-06 16:20 ` Avi Kivity
2010-04-07 6:18 ` john cooper
2010-04-08 3:33 ` Darren Hart
2010-04-09 5:52 ` john cooper
2010-04-06 16:54 ` Alan Cox
2010-04-06 18:15 ` Thomas Gleixner
2010-04-06 16:44 ` Alan Cox
2010-04-06 17:34 ` Ulrich Drepper
2010-04-10 23:35 ` Alan Cox
2010-04-10 23:53 ` Ulrich Drepper
2010-04-06 19:31 ` Thomas Gleixner
2010-04-06 20:02 ` Ulrich Drepper
2010-04-06 23:16 ` Thomas Gleixner
2010-04-06 23:36 ` Darren Hart
2010-04-07 6:08 ` drepper
2010-04-08 3:41 ` Darren Hart
2010-04-08 4:29 ` drepper
2010-04-07 5:33 ` Avi Kivity
2010-04-06 21:22 ` Darren Hart
2010-04-05 23:15 ` Darren Hart
2010-04-05 23:29 ` Chris Wright
2010-04-06 13:30 ` Avi Kivity
2010-04-06 8:48 ` Peter Zijlstra
2010-04-06 14:47 ` Ulrich Drepper
2010-04-06 14:51 ` Peter Zijlstra
2010-04-06 15:33 ` Darren Hart
2010-04-06 15:37 ` Peter Zijlstra
2010-04-06 15:29 ` Peter Zijlstra
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