Date: Fri, 10 Dec 2010 15:45:15 -0600 (CST)
From: Christoph Lameter <cl@linux.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
cc: Peter Zijlstra <peterz@infradead.org>,
        Venkatesh Pallipadi <venki@google.com>,
        Russell King - ARM Linux <linux@arm.linux.org.uk>,
        Mikael Pettersson <mikpe@it.uu.se>, Ingo Molnar <mingo@elte.hu>,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        John Stultz <johnstul@us.ibm.com>
Subject: Re: [BUG] 2.6.37-rc3 massive interactivity regression on ARM
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On Fri, 10 Dec 2010, Eric Dumazet wrote:

> > There is certainly a major difference in that execution of a stream of
> > instructions on the same cpu is guaranteed to have a coherent view of
> > the data. That is not affected by interrupts etc.
> >
>
> We dont care of interrupts. We care of doing a transaction over a
> complex set of data, that cannot be done using an atomic op (or we need
> a spinlock/mutex/rwlock), and should not because of performance.

So what? The cpu gives you incoherent view of data somewhere when only
processing data from a single cpu?

If you have remote data accesses (loop summing the data?) and you have to
be concerned about data coherence then you CANNOT use this_cpu_ops since
they are not guaranteed to be coherent to other processors.
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