Re: [PATCH 0/2] cpustat: use atomic operations to read/update stats
From: Ingo Molnar
Date: Fri Feb 22 2013 - 09:18:22 EST
* Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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
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