Re: [PATCH 1/5] ftrace: Synchronize variable setting with breakpoints

[Peter Zijlstra <peterz@infradead.org>]

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?