From: Jeremy Fitzhardinge <jeremy@goop.org>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>,
Peter Zijlstra <peterz@infradead.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Nick Piggin <npiggin@suse.de>, Jan Beulich <JBeulich@novell.com>,
Avi Kivity <avi@redhat.com>,
Xen-devel <xen-devel@lists.xensource.com>,
Linux Virtualization <virtualization@lists.linux-foundation.org>,
Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Subject: Re: [PATCH 00/20] x86: ticket lock rewrite and paravirtualization
Date: Fri, 12 Nov 2010 14:17:08 -0800 [thread overview]
Message-ID: <4CDDBCE4.80906@goop.org> (raw)
In-Reply-To: <4CDDBBD3.5050903@zytor.com>
On 11/12/2010 02:12 PM, H. Peter Anvin wrote:
> On 11/03/2010 07:59 AM, Jeremy Fitzhardinge wrote:
>> - with an unmodified struct spinlock, it can check to see if
>> head == tail after unlock; if not, then there's someone else
>> trying to lock, and we can do a kick. Unfortunately this
>> generates very high level of redundant kicks, because the
>> waiting CPU might not have blocked yet (which is the common
>> case)
>>
> How high is "very high" here -- most of the time (so that any mitigation
> on the slow patch is useless)?
I'll need to remeasure, but I think around 90% of the slowpath entries
were spurious without this. In other words, when spinlocks do contend,
most of the time it isn't very serious and the other cpu doesn't spend
much time spinning.
J
next prev parent reply other threads:[~2010-11-12 22:17 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-11-03 14:59 [PATCH 00/20] x86: ticket lock rewrite and paravirtualization Jeremy Fitzhardinge
2010-11-03 14:59 ` [PATCH 01/20] x86/ticketlock: clean up types and accessors Jeremy Fitzhardinge
2010-11-13 9:57 ` Américo Wang
2010-11-15 19:36 ` Jeremy Fitzhardinge
2010-11-03 14:59 ` [PATCH 02/20] x86/ticketlock: convert spin loop to C Jeremy Fitzhardinge
2010-11-03 15:11 ` Eric Dumazet
2010-11-03 15:38 ` Jeremy Fitzhardinge
2010-11-03 14:59 ` [PATCH 03/20] x86/ticketlock: Use C for __ticket_spin_unlock Jeremy Fitzhardinge
2010-11-03 15:13 ` Eric Dumazet
2010-11-03 18:00 ` Jeremy Fitzhardinge
2010-11-13 10:05 ` Américo Wang
2010-11-13 22:34 ` Paolo Bonzini
2010-11-15 19:38 ` Jeremy Fitzhardinge
2010-11-03 14:59 ` [PATCH 04/20] x86/ticketlock: make large and small ticket versions of spin_lock the same Jeremy Fitzhardinge
2010-11-12 12:19 ` Srivatsa Vaddagiri
2010-11-12 16:27 ` Jeremy Fitzhardinge
2010-11-03 14:59 ` [PATCH 05/20] x86/ticketlock: make __ticket_spin_lock common Jeremy Fitzhardinge
2010-11-03 14:59 ` [PATCH 06/20] x86/ticketlock: make __ticket_spin_trylock common Jeremy Fitzhardinge
2010-11-13 10:17 ` Américo Wang
2010-11-13 10:48 ` Eric Dumazet
2010-11-15 19:39 ` Jeremy Fitzhardinge
2010-11-03 14:59 ` [PATCH 07/20] x86/spinlocks: replace pv spinlocks with pv ticketlocks Jeremy Fitzhardinge
2010-11-03 14:59 ` [PATCH 08/20] x86/ticketlock: collapse a layer of functions Jeremy Fitzhardinge
2010-11-03 14:59 ` [PATCH 09/20] xen/pvticketlock: Xen implementation for PV ticket locks Jeremy Fitzhardinge
2010-11-03 14:59 ` [PATCH 10/20] x86/pvticketlock: keep count of blocked cpus Jeremy Fitzhardinge
2010-11-03 14:59 ` [PATCH 11/20] x86/pvticketlock: use callee-save for lock_spinning Jeremy Fitzhardinge
2010-11-03 14:59 ` [PATCH 12/20] x86/pvticketlock: use callee-save for unlock_kick as well Jeremy Fitzhardinge
2010-11-03 14:59 ` [PATCH 13/20] x86/pvticketlock: make sure unlock is seen by everyone before checking waiters Jeremy Fitzhardinge
2010-11-03 14:59 ` [PATCH 14/20] x86/ticketlock: loosen ordering restraints on unlock Jeremy Fitzhardinge
2010-11-03 14:59 ` [PATCH 15/20] x86/ticketlock: prevent compiler reordering into locked region Jeremy Fitzhardinge
2010-11-03 14:59 ` [PATCH 16/20] x86/ticketlock: don't inline _spin_unlock when using paravirt spinlocks Jeremy Fitzhardinge
2010-11-03 14:59 ` [PATCH 17/20] x86/ticketlock: clarify barrier in arch_spin_lock Jeremy Fitzhardinge
2010-11-03 14:59 ` [PATCH 18/20] x86/ticketlock: remove .slock Jeremy Fitzhardinge
2010-11-03 15:00 ` [PATCH 19/20] x86/ticketlocks: use overlapping read to eliminate mb() Jeremy Fitzhardinge
2010-11-03 15:00 ` [PATCH 20/20] x86/ticketlock: rename ticketpair to head_tail Jeremy Fitzhardinge
2010-11-12 22:12 ` [PATCH 00/20] x86: ticket lock rewrite and paravirtualization H. Peter Anvin
2010-11-12 22:17 ` Jeremy Fitzhardinge [this message]
2010-11-12 22:20 ` H. Peter Anvin
2010-11-15 20:00 ` Jeremy Fitzhardinge
2010-11-15 20:03 ` H. Peter Anvin
2010-11-15 20:14 ` Peter Zijlstra
2010-11-15 21:02 ` Jeremy Fitzhardinge
2010-11-15 21:08 ` Peter Zijlstra
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