From: Rik van Riel <riel@redhat.com>
To: Andi Kleen <andi@firstfloor.org>
Cc: Jiannan Ouyang <ouyang@cs.pitt.edu>,
LKML <linux-kernel@vger.kernel.org>,
Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
Peter Zijlstra <peterz@infradead.org>,
Avi Kivity <avi.kivity@gmail.com>, Gleb Natapov <gleb@redhat.com>,
Ingo Molnar <mingo@redhat.com>,
Marcelo Tosatti <mtosatti@redhat.com>,
Srikar <srikar@linux.vnet.ibm.com>,
"H. Peter Anvin" <hpa@zytor.com>,
"Nikunj A. Dadhania" <nikunj@linux.vnet.ibm.com>,
KVM <kvm@vger.kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
Chegu Vinod <chegu_vinod@hp.com>,
"Andrew M. Theurer" <habanero@linux.vnet.ibm.com>,
Srivatsa Vaddagiri <srivatsa.vaddagiri@gmail.com>,
Andrew Jones <drjones@redhat.com>, Karen Noel <knoel@redhat.com>
Subject: Re: Preemptable Ticket Spinlock
Date: Mon, 22 Apr 2013 19:13:48 -0400 [thread overview]
Message-ID: <5175C42C.1030901@redhat.com> (raw)
In-Reply-To: <m2k3nuw7oj.fsf@firstfloor.org>
On 04/22/2013 05:56 PM, Andi Kleen wrote:
> Rik van Riel <riel@redhat.com> writes:
>>
>> If we always incremented the ticket number by 2 (instead of 1), then
>> we could use the lower bit of the ticket number as the spinlock.
>
> Spinning on a single bit is very inefficient, as you need to do
> try lock in a loop which is very unfriendly to the MESI state protocol.
> It's much better to have at least three states and allow
> spinning-while-reading-only.
>
> This is typically very visible on systems with >2S.
Absolutely, the spinning should be read-only, until the CPU
sees that the desired bit is clear. MESI-friendly spinning
is essential.
--
All rights reversed
next prev parent reply other threads:[~2013-04-22 23:13 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CAJocwccu5QQyuKRvgNyPSFz2K_rzCW419W9-XdSUYOL7+KqQKg@mail.gmail.com>
2013-04-21 21:12 ` Preemptable Ticket Spinlock Rik van Riel
2013-04-21 23:07 ` Jiannan Ouyang
2013-04-22 5:59 ` Raghavendra K T
2013-04-22 11:51 ` Peter Zijlstra
2013-04-22 12:52 ` Rik van Riel
2013-04-22 19:49 ` Peter Zijlstra
2013-04-22 19:56 ` Rik van Riel
2013-04-22 20:05 ` Jiannan Ouyang
2013-04-22 20:08 ` Peter Zijlstra
2013-04-22 20:32 ` Rik van Riel
2013-04-22 20:44 ` Peter Zijlstra
2013-04-22 20:48 ` Peter Zijlstra
2013-04-22 20:50 ` Rik van Riel
2013-04-22 20:50 ` Jiannan Ouyang
2013-04-22 20:54 ` Chegu Vinod
2013-04-22 20:46 ` Jiannan Ouyang
2013-04-22 20:49 ` Rik van Riel
2013-04-22 21:01 ` Peter Zijlstra
2013-04-23 5:03 ` Raghavendra K T
2013-04-22 20:55 ` Peter Zijlstra
2013-04-22 21:31 ` Jiannan Ouyang
2013-04-22 23:08 ` Rik van Riel
2013-04-23 5:57 ` Gleb Natapov
2013-04-23 1:42 ` Raghavendra K T
2013-05-30 11:56 ` Raghavendra K T
2013-05-30 20:14 ` Thomas Gleixner
2013-04-22 21:56 ` Andi Kleen
2013-04-22 23:13 ` Rik van Riel [this message]
2013-04-22 5:58 ` Raghavendra K T
2013-04-22 16:42 ` Jiannan Ouyang
2013-04-23 1:54 ` Raghavendra K T
2013-04-26 20:10 ` Andrew Theurer
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