[PATCH 0/2] cpustat: use atomic operations to read/update stats

[Ingo Molnar]

* Peter Zijlstra <peterz at infradead.org> wrote:

> On Fri, 2013-02-22 at 13:50 +0100, Frederic Weisbecker wrote:
> > > Argh!! at what cost? 64bit atomics are like expensive. Wouldn't
> > adding
> > > a seqlock be saner?
> > 
> > Not sure. This requires a spinlock in the write side which is called
> > from
> > fast path like the timer interrupt.
> 
> A single spinlock is _way_ cheaper than a ton of cmpxchg8b()s 
> to update a few variables.

Every cmpxchg8b() will be roughly as expensive as a spinlock 
acquire+release fastpath.

Thanks,

	Ingo