Re: [RFC][PATCH 2/5] mm: Switch mod_state() to __this_cpu_read()
From: Christoph Lameter
Date: Tue Sep 20 2011 - 12:07:32 EST
On Tue, 20 Sep 2011, Steven Rostedt wrote:
> > NO!! This defeats the whole purpose of this_cpu_ops and make the whole
> > scheme utterly useless.
>
> The thing is, the whole purpose was broken to begin with. Defeating a
> broken design is a good thing!
So then we are not allowed to use segment prefixes in core code to avoid
preempt enable disable? And to avoid interrupt disabling enabling in
critical allocator sections?
> > There are trivial cases like counter increments that are not a problem at
> > all. Most use cases are those. More complex ones can be developed to avoid
> > various overhead in performance critical sections of the kernel.
> >
>
> And adding a preempt_disable; this_cpu_inc(); preempt_enable; is not a
> bad thing either.
It defeats the purpose of the whole thing.
> What benchmarks do you have that shows this helped in anything????
The various patchsets that went into the kernel had benchmarks results.
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