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
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=4E134E1E.6040304@zytor.com \
--to=hpa@zytor.com \
--cc=JBeulich@novell.com \
--cc=a.p.zijlstra@chello.nl \
--cc=brgerst@gmail.com \
--cc=fweisbec@gmail.com \
--cc=gorcunov@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@elte.hu \
--cc=tglx@linutronix.de \
/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.