From: "H. Peter Anvin" <hpa@zytor.com>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Christoph Lameter <cl@linux.com>, Tejun Heo <tj@kernel.org>,
akpm@linux-foundation.org, Pekka Enberg <penberg@cs.helsinki.fi>,
linux-kernel@vger.kernel.org,
Eric Dumazet <eric.dumazet@gmail.com>,
Arjan van de Ven <arjan@infradead.org>
Subject: Re: [cpuops cmpxchg V1 2/4] x86: this_cpu_cmpxchg and this_cpu_xchg operations
Date: Wed, 08 Dec 2010 22:26:59 -0800 [thread overview]
Message-ID: <4D0076B3.9090106@zytor.com> (raw)
In-Reply-To: <20101208181736.GC30693@Krystal>
On 12/08/2010 10:17 AM, Mathieu Desnoyers wrote:
>
> Hi Christoph,
>
> Can you show if this provides savings in terms of:
>
> - instruction cache footprint
> - cycles required to run
> - large-scale impact on the branch prediction buffers
>
> Given that this targets per-cpu data only, the additional impact on cache-line
> exchange traffic of using cmpxchg over xchg (cache-line not grabbed as exclusive
> by the initial read) should not really matter.
>
> I'm CCing Arjan and HPA, because they might have some interesting insight into
> the performance impact of lock-prefixed xchg vs using local cmpxchg in a loop.
>
XCHG is always locked; it doesn't need the prefix. Unfortunately,
unlike on the 8086 on modern processors locks have a real cost.
-hpa
--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.
next prev parent reply other threads:[~2010-12-09 6:29 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-12-08 17:55 [cpuops cmpxchg V1 0/4] Cmpxchg and xchg operations Christoph Lameter
2010-12-08 17:55 ` [cpuops cmpxchg V1 1/4] percpu: Generic this_cpu_cmpxchg() and this_cpu_xchg support Christoph Lameter
2010-12-08 17:55 ` [cpuops cmpxchg V1 2/4] x86: this_cpu_cmpxchg and this_cpu_xchg operations Christoph Lameter
2010-12-08 18:08 ` Christoph Lameter
2010-12-08 18:17 ` Mathieu Desnoyers
2010-12-09 6:26 ` H. Peter Anvin [this message]
2010-12-09 23:40 ` Christoph Lameter
2010-12-08 22:20 ` Christoph Lameter
2010-12-08 17:55 ` [cpuops cmpxchg V1 3/4] irq_work: Use per cpu atomics instead of regular atomics Christoph Lameter
2010-12-08 17:55 ` [cpuops cmpxchg V1 4/4] vmstat: User per cpu atomics to avoid interrupt disable / enable Christoph Lameter
2010-12-08 22:22 ` cpuops cmpxchg: Provide 64 bit this_cpu_xx for 32 bit x86 using cmpxchg8b Christoph Lameter
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