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SubjectRe: [cpuops cmpxchg V2 3/5] irq_work: Use per cpu atomics instead of regular atomics
FromPeter Zijlstra <>
DateWed, 15 Dec 2010 17:50:39 +0100
On Wed, 2010-12-15 at 17:32 +0100, Tejun Heo wrote:
> On 12/14/2010 05:28 PM, Christoph Lameter wrote:
> > The irq work queue is a per cpu object and it is sufficient for
> > synchronization if per cpu atomics are used. Doing so simplifies
> > the code and reduces the overhead of the code.
> >
> > Before:
> >
> > christoph@linux-2.6$ size kernel/irq_work.o
> > text data bss dec hex filename
> > 451 8 1 460 1cc kernel/irq_work.o
> >
> > After:
> >
> > christoph@linux-2.6$ size kernel/irq_work.o
> > text data bss dec hex filename
> > 438 8 1 447 1bf kernel/irq_work.o
> >
> > Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
>
> Peter, can you please ack this one?

I guess so, I don't much like the bare preempt_disable/enable there, and
I'm wondering, aren't %fs prefixed insn slower than regular insn? Does
it really pay to avoid this one address computation if there's multiple
users in a function. %fs prefixes do take another byte, so it will also
result in larger code at some point.


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