Subject: Re: [PATCH] [2/2] POWERPC: Lower threshold for DART enablement to 1GB, V2

From: Benjamin Herrenschmidt <[email-masked]>
Date: Fri, 14 Apr 2006 08:38:31 +1000

On Thu, 2006-04-13 at 17:27 -0500, Olof Johansson wrote:
> On Fri, Apr 14, 2006 at 06:51:55AM +1000, Benjamin Herrenschmidt wrote:
> 
> > an improvement with the DART thanks to virtual merging. Currently, we
> > pay a cost due to our stupid invalidate mecanism that we should really
> > fix by shooting the TLB directly.
> 
> What was keeping me from implementing this before was the lack of public
> documentation on how to do it. Has that changed? I'd be happy to do the
> implementation.

Darwin has the macros to access the TLB though it doesn't use them... I
suppose I can get the necessary doco bit from the microelectronics folks
for the CPC925, that should apply to U3 as well, though U4 has a
different format afaik. I'll dig and will come back to you.

> > Also have you made sure all your
> > additions for handling crappy hardware are nicely wrapped in unlikely()
> > statements ? :)
> 
> I would expect the dynamic predictor to work quite well on this. I'm not
> worried about the overhead of the tests as much as the overhead of
> having to enable the DART for smaller configs. If benchmark profiling
> shows different down the road then we can add them.

Ok.

Ben.