linux-kernel - Re: [PATCH 0/2] Add percpu smp cacheline align section

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Message-ID: <20070507171129.GA21638@linux-os.sc.intel.com>
Date:	Mon, 7 May 2007 10:11:29 -0700
From:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
To:	Christoph Lameter <clameter@....com>
Cc:	"Yu, Fenghua" <fenghua.yu@...el.com>, akpm@...ux-foundation.org,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] Add percpu smp cacheline align section

On Sat, May 05, 2007 at 09:52:27AM -0700, Christoph Lameter wrote:
> On Fri, 4 May 2007, Fenghua Yu wrote:
>
> > This is follow-up for Suresh's runqueue align in smp patch at:
> > [1]http://www.uwsg.iu.edu/hypermail/linux/kernel/0704.1/0340.html
> >
> > The patches place all of smp cacheline aligned percpu data into
> > .data.percpu.cacheline_aligned_in_smp. Other percpu data is still in
> > data.percpu section. The patches can reduce cache line access in SMP and
> > reduce alignment gap waste. The patches also define PERCPU macro for
> > vmlinux.lds.S for code clean up.
>
> Ummm... The per cpu area is for exclusive use of a particular processor.
> If there is contention in the per cpu area then a data object needs to be
> removed from the per cpu area because the object is *not* accessed only
> from a certain cpu.

Christoph, This data(that is being accessed by other cpus) also needs
to be defined for each cpu and as such it is getting appended (and
clearly seperated in a different section) to the data which is accessed
only by the local cpu.

Not sure what your concern is.

thanks,
suresh
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