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SubjectRe: [PATCH 1/5] ftrace: Synchronize variable setting with breakpoints
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On Thu, 2012-05-31 at 16:37 -0400, Steven Rostedt wrote:
> On Thu, 2012-05-31 at 22:26 +0200, Peter Zijlstra wrote:
>
> > Right, but when you loose stop-machine you could simply do 30k
> > kmap_atomic/kunmap_atomic's consecutively since you're not holding
> > anybody up.
>
> It requires 3 IPIs per update too. Thus that's 90,000 IPIs you are
> blasting^Wsending to all CPUs.

Uhm, no.

for_each() {
kmap_atomic()
frob int3
kunmap_atomic();
}
sync-ipi-broadcast();

for_each() {
kmap_atomic();
frob tail
kunmap_atomic();
}
sync-ipi-broadcast();

for_each() {
kmap_atomic();
frob head
kunmap_atomic();
};
sync-ipi-broadcast();

How is that sending 90k ipis?


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