From: "H. Peter Anvin" <hpa@zytor.com>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
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>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Subject: Re: [cpuops cmpxchg V2 3/5] irq_work: Use per cpu atomics instead of regular atomics
Date: Wed, 15 Dec 2010 09:31:14 -0800 [thread overview]
Message-ID: <4D08FB62.9070104@zytor.com> (raw)
In-Reply-To: <1292433517.2708.41.camel@laptop>
On 12/15/2010 09:18 AM, Peter Zijlstra wrote:
> On Wed, 2010-12-15 at 11:04 -0600, Christoph Lameter wrote:
>
>> Prefixes are faster than explicit address calculations. A prefix allows
>> you to integrate the per cpu address calculation into an arithmetic
>> operation.
>
> Well, depends on how often you need that address I'd think. If you'd
> have a per-cpu struct and need to frob lots of variables in that struct
> it might be cheaper to simply compute the struct address once and then
> use relative addresses than to prefix everything with %fs.
>
Let's just make it clear -- current x86 CPUs generally do not have a
penalty for prefixes (it might be that under very unusual pipeline
conditions they do, I am not 100% sure.) In fact, we changed patching
LOCK prefixes from NOP to %ds: because it made the code faster.
Some older CPUs do, but those are no longer relevant for performance
decisions.
-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:[~2010-12-15 17:32 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-12-14 16:28 [cpuops cmpxchg V2 0/5] Cmpxchg and xchg operations Christoph Lameter
2010-12-14 16:28 ` [cpuops cmpxchg V2 1/5] percpu: Generic this_cpu_cmpxchg() and this_cpu_xchg support Christoph Lameter
2010-12-17 14:55 ` Tejun Heo
2010-12-14 16:28 ` [cpuops cmpxchg V2 2/5] x86: this_cpu_cmpxchg and this_cpu_xchg operations Christoph Lameter
2010-12-17 15:22 ` Tejun Heo
2010-12-14 16:28 ` [cpuops cmpxchg V2 3/5] irq_work: Use per cpu atomics instead of regular atomics Christoph Lameter
2010-12-15 16:32 ` Tejun Heo
2010-12-15 16:34 ` H. Peter Anvin
2010-12-15 16:50 ` Peter Zijlstra
2010-12-15 17:04 ` Christoph Lameter
2010-12-15 17:18 ` Peter Zijlstra
2010-12-15 17:31 ` H. Peter Anvin [this message]
2010-12-15 17:32 ` Christoph Lameter
2010-12-18 15:32 ` Tejun Heo
2010-12-14 16:28 ` [cpuops cmpxchg V2 4/5] vmstat: User per cpu atomics to avoid interrupt disable / enable Christoph Lameter
2010-12-15 16:45 ` Tejun Heo
2010-12-15 17:01 ` Christoph Lameter
2010-12-14 16:28 ` [cpuops cmpxchg V2 5/5] cpuops: Use cmpxchg for xchg to avoid lock semantics Christoph Lameter
2010-12-14 16:35 ` Mathieu Desnoyers
2010-12-14 16:44 ` Eric Dumazet
2010-12-14 16:55 ` Christoph Lameter
2010-12-14 17:00 ` H. Peter Anvin
2010-12-14 17:19 ` Christoph Lameter
2010-12-14 17:22 ` H. Peter Anvin
2010-12-14 17:29 ` Tejun Heo
2010-12-14 17:35 ` Christoph Lameter
2010-12-15 1:06 ` H. Peter Anvin
2010-12-15 16:29 ` Tejun Heo
2010-12-15 16:35 ` H. Peter Anvin
2010-12-15 16:39 ` Tejun Heo
2010-12-16 16:14 ` Tejun Heo
2010-12-16 18:13 ` x86: Use this_cpu_has for thermal_interrupt Christoph Lameter
2010-12-18 15:35 ` Tejun Heo
2010-12-21 0:56 ` H. Peter Anvin
2010-12-30 11:29 ` Tejun Heo
2010-12-30 18:19 ` H. Peter Anvin
2010-12-31 12:43 ` Tejun Heo
2010-12-16 18:14 ` x86: udelay: Use this_cpu_read to avoid address calculation Christoph Lameter
2010-12-16 18:15 ` gameport: use this_cpu_read instead of lookup Christoph Lameter
2010-12-18 15:34 ` Tejun Heo
2010-12-16 18:16 ` acpi throttling: Use this_cpu_has and simplify code Christoph Lameter
2010-12-18 15:50 ` Tejun Heo
2010-12-21 1:52 ` ykzhao
2010-12-21 22:43 ` Christoph Lameter
2010-12-21 4:28 ` Len Brown
2010-12-16 18:19 ` [cpuops cmpxchg V2 5/5] cpuops: Use cmpxchg for xchg to avoid lock semantics H. Peter Anvin
2010-12-16 18:55 ` Tejun Heo
2010-12-16 20:42 ` H. Peter Anvin
2010-12-15 16:47 ` Tejun Heo
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=4D08FB62.9070104@zytor.com \
--to=hpa@zytor.com \
--cc=a.p.zijlstra@chello.nl \
--cc=akpm@linux-foundation.org \
--cc=cl@linux.com \
--cc=eric.dumazet@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mathieu.desnoyers@efficios.com \
--cc=penberg@cs.helsinki.fi \
--cc=tj@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.