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From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Andi Kleen <andi@firstfloor.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Huang Ying <ying.huang@intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 8/5] llist: Remove cpu_relax() usage in cmpxchg loops
Date: Mon, 12 Sep 2011 10:47:06 -0400	[thread overview]
Message-ID: <20110912144706.GA21716@Krystal> (raw)
In-Reply-To: <20110912142305.GN7761@one.firstfloor.org>

* Andi Kleen (andi@firstfloor.org) wrote:
> On Mon, Sep 12, 2011 at 04:05:58PM +0200, Peter Zijlstra wrote:
> > Subject: llist: Remove cpu_relax() usage in cmpxchg loops
> > From: Peter Zijlstra <a.p.zijlstra@chello.nl>
> > Date: Mon Sep 12 15:50:49 CEST 2011
> > 
> > Initial benchmarks show they're a net loss (2 socket wsm):
> > 
> 
> May still save power.

Looking at kernel/spinlock.c:

void __lockfunc __raw_##op##_lock(locktype##_t *lock) \
{
[...]
                while (!raw_##op##_can_lock(lock) && (lock)->break_lock)\
                        arch_##op##_relax(&lock->raw_lock); \

so basically, in typical locking primitives (spinlock), it looks like
lower power consumption is preferred over getting the raw maximal
performance in fully contented scenarios.

So what is the rationale for making those lock-less lists retry scheme
different from spinlocks here ?

Thanks,

Mathieu

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com

  parent reply	other threads:[~2011-09-12 14:47 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-09-08  6:00 [PATCH -mm -v2 0/5] irq_work, Use llist in irq_work Huang Ying
2011-09-08  6:00 ` [PATCH -mm -v2 1/5] llist, Make all llist functions inline Huang Ying
2011-09-08  6:00 ` [PATCH -mm -v2 2/5] llist, Define macro to check NMI safe cmpxchg Huang Ying
2011-09-08  6:00 ` [PATCH -mm -v2 3/5] llist, Move cpu_relax after cmpxchg Huang Ying
2011-09-08  6:00 ` [PATCH -mm -v2 4/5] llist, Return whether list is empty before adding in llist_add Huang Ying
2011-09-08  6:00 ` [PATCH -mm -v2 5/5] irq_work, Use llist in irq_work Huang Ying
2011-09-12 14:05 ` [PATCH 6/5] llist: Add llist_next() Peter Zijlstra
2011-09-12 14:05 ` [PATCH 7/5] sched: Convert to use llist Peter Zijlstra
2011-09-12 14:05 ` [PATCH 8/5] llist: Remove cpu_relax() usage in cmpxchg loops Peter Zijlstra
2011-09-12 14:23   ` Andi Kleen
2011-09-12 14:23     ` Peter Zijlstra
2011-09-12 14:47     ` Mathieu Desnoyers [this message]
2011-09-12 15:09       ` Peter Zijlstra
2011-09-12 15:24       ` Peter Zijlstra
2011-09-12 16:38       ` Andi Kleen
2011-09-12 18:53         ` Peter Zijlstra
2011-09-12 14:26   ` Avi Kivity
2011-09-12 14:32     ` Peter Zijlstra
2011-09-13 11:43       ` Avi Kivity
2011-09-13 14:22         ` Peter Zijlstra
2011-09-13 14:51           ` Avi Kivity
2011-09-13 14:53             ` Peter Zijlstra
2011-09-12 14:06 ` [PATCH -mm -v2 0/5] irq_work, Use llist in irq_work Peter Zijlstra

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