From: Ian Campbell <ijc@hellion.org.uk>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>,
LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>,
Thomas Gleixner <tglx@linutronix.de>,
Brian Gerst <brgerst@gmail.com>,
Jan Beulich <JBeulich@novell.com>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: [Q x86-64] on kernel_eflags
Date: Wed, 06 Jul 2011 10:25:38 +0100 [thread overview]
Message-ID: <1309944338.634.162.camel@zakaz.uk.xensource.com> (raw)
In-Reply-To: <4E134E1E.6040304@zytor.com>
On Tue, 2011-07-05 at 10:47 -0700, H. Peter Anvin wrote:
> On 07/05/2011 03:47 AM, Cyrill Gorcunov wrote:
> >
> > Should not every cpu has own copy of kernel_eflags? Just
> > to be consistent in style? Or this would be space waisting
> > and an optimization is done here?
> >
>
> Not specific to this particular case, but in general: a shared variable
> that used often but rarely written to will automatically replicate
> itself in the caches of multiple processors. This is the purpose of the
> read_mostly segment (writes are permitted but expected to be rare),
> which exists to make sure that a frequently written variable doesn't
> randomly end up in the cache line next to a read-mostly variable.
FWIW the variable in this particular case isn't actually marked as
__read_mostly...
Ian.
--
Ian Campbell
* Simunye is on a oc3->oc12
simmy: bite me. :)
daemon: okay :)
prev parent reply other threads:[~2011-07-06 9:25 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-07-05 10:47 Cyrill Gorcunov
2011-07-05 11:00 ` Ian Campbell
2011-07-05 11:15 ` Cyrill Gorcunov
2011-07-05 13:00 ` [PATCH 1/3] x86: drop unnecessary kernel_eflags variable from 64 bit Ian Campbell
2011-07-05 13:28 ` Cyrill Gorcunov
2011-07-06 9:25 ` Ian Campbell
2011-07-06 9:46 ` Cyrill Gorcunov
2011-07-06 9:57 ` Ian Campbell
2011-07-06 10:12 ` Cyrill Gorcunov
2011-07-06 9:39 ` Pekka Enberg
2011-07-06 23:17 ` Andi Kleen
2011-07-07 0:00 ` H. Peter Anvin
2011-07-05 13:00 ` [PATCH 2/3] x86: make 64 bit ret_from_fork a little more similar to 32 bit Ian Campbell
2011-07-06 9:41 ` Pekka Enberg
2011-07-05 13:00 ` [PATCH 3/3] x86: ret_from_fork: use symbolic contants for bits in EFLAGS Ian Campbell
2011-07-06 9:36 ` Pekka Enberg
2011-07-05 17:47 ` [Q x86-64] on kernel_eflags H. Peter Anvin
2011-07-05 17:56 ` Cyrill Gorcunov
2011-07-06 9:25 ` Ian Campbell [this message]
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