Re: [PATCH] cpuacct: add a branch prediction

[Paul Mackerras]

Ingo Molnar writes:

> * Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> wrote:
> 
> > On Thu, 2009-02-26 at 21:06 +0900, KAMEZAWA Hiroyuki wrote:
> > > Hmm.. some routine like
> > > atomic64_read() can help this ? (But I don't want to use atomic_t here..)
> > 
> > Yeah, atomic64_t has been proposed numerous times, and x86 
> > could actually implement that using cmpxchg8b, just not sure 
> > about all the other 32bit archs, and if we start using it in 
> > the scheduler, they'd better have it implemented.
> 
> I have written a working atomic64_t implementation for 
> tip:perfcounters/core, for 32-bit x86.

atomic64_t would be a big problem for 32-bit powerpc.  We'd have to
use an array of spinlocks, or make atomic64_t actually be 12 bytes so
we have a lock word to use.

Paul.
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