From: Paolo Bonzini <pbonzini@redhat.com>
To: Waiman Long <waiman.long@hp.com>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>,
tglx@linutronix.de, mingo@kernel.org, linux-arch@vger.kernel.org,
linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org,
xen-devel@lists.xenproject.org, kvm@vger.kernel.org,
paolo.bonzini@gmail.com, boris.ostrovsky@oracle.com,
paulmck@linux.vnet.ibm.com, riel@redhat.com,
torvalds@linux-foundation.org, raghavendra.kt@linux.vnet.ibm.com,
david.vrabel@citrix.com, oleg@redhat.com, gleb@redhat.com,
scott.norton@hp.com, chegu_vinod@hp.com,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 04/11] qspinlock: Extract out the exchange of tail code word
Date: Wed, 18 Jun 2014 17:49:52 +0200 [thread overview]
Message-ID: <53A1B520.6090902@redhat.com> (raw)
In-Reply-To: <53A1B43C.8000009@hp.com>
Il 18/06/2014 17:46, Waiman Long ha scritto:
>>
>>
>> The #1 patch is nice by itself - as it lays out the foundation of the
>> MCS-similar code - and if Ingo decides he does not want this pending
>> byte-lock bit business - it can be easily reverted or dropped.
>
> The pending bit code is needed for performance parity with ticket
> spinlock for light load. My own measurement indicates that the queuing
> overhead will cause the queue spinlock to be slower than ticket spinlock
> with 2-4 contending tasks. The pending bit solves the performance
> problem with 2 contending tasks, leave only the 3-4 tasks cases being a
> bit slower than the ticket spinlock which should be more than
> compensated by its superior performance with heavy contention and
> slightly better performance with no contention.
Note that this patch is not related to the pending bit, only to the
trylock bit which is already in patch 1. It serializes two
previously-parallel checks for transitions. This is why I thought it
could already belong in patch 1.
Paolo
next prev parent reply other threads:[~2014-06-18 15:50 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-15 12:46 [PATCH 00/11] qspinlock with paravirt support Peter Zijlstra
2014-06-15 12:46 ` [PATCH 01/11] qspinlock: A simple generic 4-byte queue spinlock Peter Zijlstra
2014-06-16 20:49 ` Konrad Rzeszutek Wilk
2014-06-17 20:03 ` Konrad Rzeszutek Wilk
2014-06-23 16:12 ` Peter Zijlstra
2014-06-23 16:20 ` Konrad Rzeszutek Wilk
2014-06-23 15:56 ` Peter Zijlstra
2014-06-23 16:16 ` Konrad Rzeszutek Wilk
2014-06-17 20:05 ` Konrad Rzeszutek Wilk
2014-06-23 16:26 ` Peter Zijlstra
2014-06-23 16:45 ` Konrad Rzeszutek Wilk
2014-06-15 12:46 ` [PATCH 02/11] qspinlock, x86: Enable x86-64 to use " Peter Zijlstra
2014-06-15 12:47 ` [PATCH 03/11] qspinlock: Add pending bit Peter Zijlstra
2014-06-17 20:36 ` Konrad Rzeszutek Wilk
2014-06-17 20:51 ` Waiman Long
2014-06-17 21:07 ` Konrad Rzeszutek Wilk
2014-06-17 21:10 ` Konrad Rzeszutek Wilk
2014-06-17 22:25 ` Waiman Long
2014-06-24 8:24 ` Peter Zijlstra
2014-06-18 11:29 ` Paolo Bonzini
2014-06-18 13:36 ` Konrad Rzeszutek Wilk
2014-06-23 16:35 ` Peter Zijlstra
2014-06-15 12:47 ` [PATCH 04/11] qspinlock: Extract out the exchange of tail code word Peter Zijlstra
2014-06-17 20:55 ` Konrad Rzeszutek Wilk
2014-06-18 11:37 ` Paolo Bonzini
2014-06-18 13:50 ` Konrad Rzeszutek Wilk
2014-06-18 15:46 ` Waiman Long
2014-06-18 15:49 ` Paolo Bonzini [this message]
2014-06-18 16:02 ` Konrad Rzeszutek Wilk
2014-06-24 10:47 ` Peter Zijlstra
2014-06-15 12:47 ` [PATCH 05/11] qspinlock: Optimize for smaller NR_CPUS Peter Zijlstra
2014-06-18 11:39 ` Paolo Bonzini
2014-07-07 14:35 ` Peter Zijlstra
2014-07-07 15:08 ` Paolo Bonzini
2014-07-07 15:35 ` Peter Zijlstra
2014-07-07 16:10 ` Paolo Bonzini
2014-06-18 15:57 ` Konrad Rzeszutek Wilk
2014-07-07 14:33 ` Peter Zijlstra
2014-06-15 12:47 ` [PATCH 06/11] qspinlock: Optimize pending bit Peter Zijlstra
2014-06-18 11:42 ` Paolo Bonzini
2014-06-15 12:47 ` [PATCH 07/11] qspinlock: Use a simple write to grab the lock, if applicable Peter Zijlstra
2014-06-18 16:36 ` Konrad Rzeszutek Wilk
2014-07-07 14:51 ` Peter Zijlstra
2014-06-15 12:47 ` [PATCH 08/11] qspinlock: Revert to test-and-set on hypervisors Peter Zijlstra
2014-06-16 21:57 ` Waiman Long
2014-06-18 16:40 ` Konrad Rzeszutek Wilk
2014-06-15 12:47 ` [PATCH 09/11] pvqspinlock, x86: Rename paravirt_ticketlocks_enabled Peter Zijlstra
2014-06-18 16:43 ` Konrad Rzeszutek Wilk
2014-06-15 12:47 ` [PATCH 10/11] qspinlock: Paravirt support Peter Zijlstra
2014-06-17 0:53 ` Waiman Long
2014-06-18 12:04 ` Paolo Bonzini
2014-06-20 13:46 ` Konrad Rzeszutek Wilk
2014-07-07 15:27 ` Peter Zijlstra
2014-07-15 14:23 ` Konrad Rzeszutek Wilk
[not found] ` <539F6AD5.4070301@hp.com>
2014-06-18 12:03 ` Paolo Bonzini
2014-06-18 15:26 ` Waiman Long
2014-07-07 15:20 ` Peter Zijlstra
2014-07-07 15:20 ` Peter Zijlstra
2014-06-15 12:47 ` [PATCH 11/11] qspinlock, kvm: Add paravirt support Peter Zijlstra
2014-06-22 16:36 ` Raghavendra K T
2014-07-07 15:23 ` Peter Zijlstra
2014-06-16 20:52 ` [PATCH 00/11] qspinlock with " Konrad Rzeszutek Wilk
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