From: "H. Peter Anvin" <hpa@zytor.com>
To: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: 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: Tue, 05 Jul 2011 10:47:10 -0700 [thread overview]
Message-ID: <4E134E1E.6040304@zytor.com> (raw)
In-Reply-To: <20110705104742.GO17941@sun>
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.
-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:[~2011-07-05 17:47 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-07-05 10:47 [Q x86-64] on kernel_eflags 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 ` H. Peter Anvin [this message]
2011-07-05 17:56 ` [Q x86-64] on kernel_eflags Cyrill Gorcunov
2011-07-06 9:25 ` Ian Campbell
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