linux-kernel - Re: [Q x86-64] on kernel

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Message-ID: <20110705175609.GF4060@sun>
Date:	Tue, 5 Jul 2011 21:56:09 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Brian Gerst <brgerst@...il.com>,
	Jan Beulich <JBeulich@...ell.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [Q x86-64] on kernel_eflags

On Tue, Jul 05, 2011 at 10:47:10AM -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.
> 
> 	-hpa
> 

yeah, thanks peter!

	Cyrill
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