Worst case performance of up()

Benjamin Herrenschmidt benh at kernel.crashing.org
Sun Dec 3 07:52:53 EST 2006

On Sat, 2006-12-02 at 11:54 +0000, Adrian Cox wrote:
> On Sat, 2006-12-02 at 22:15 +1100, Benjamin Herrenschmidt wrote:
> > I think we are hitting a livelock due to both CPUs trying to perform an
> > atomic operation on the same cache line (or same variable even).
> I agree.
> > Can you remind me what CPU this on precisely ? I know that for some
> > CPUs like 970's, Apple code has some weirdo workarounds around atomic
> > ops involving forcing a mispredict when the stwcx. fails ... but if both
> > CPUs are following the exact same pattern, I can't see another way out
> > but an interrupt, unless something in the bus protocol can prevent such
> > livelocks...
> It's a pair of 7448s in MPX bus mode, with a Tsi109 host bridge.

At this point, we might have good use of Freescale help... there might
be something we can do in the construct of the atomic ops to avoid


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