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Re: [PATCH] Fix build failure on power4


On Wed, 2013-01-02 at 15:18 +0100, Andreas Jaeger wrote:
> On 01/02/2013 03:14 PM, Siddhesh Poyarekar wrote:
> > On Wed, Jan 02, 2013 at 10:55:51AM -0200, Adhemerval Zanella wrote:
> >> Hi Siddhesh
> >>
> >> It fixes my builds for power4.
> >>
> >
> > Thanks for verifying.  Do I need another ack to commit this or is it
> > OK if I go right ahead?
> 
> You get my ack as well. Since it's PowerPC, normally Ryan comments but 
> seeing the change and testing done, I suggest you go ahead if he does 
> not speak up - so let's give Ryan another day to comment first and then 
> commit,
> 
Yes the whole set of patches needs to be review by the PowerPC
maintainer (and myself as the originator of the PPC specific mpa.c
changes).

This whole series make some rash assumptions about the relative
performance of FXU/FPU pipelines and the associate latencies for
transfers between them. Also the trade-offs become less obvious on
out-of-order, weakly-consistent-memory machines like PowerPC and all
POWER servers since POWER4 (POWER6 was in-order but still weakly
consistent). 

Also this implementation totally ignores the possibility for
super-scalar pipeline parallelism. This was the original rational for
the power4 specialization. This applicable to both Fixed (FXU) and
floating Point (FPU) computation.

Finally someone should look at this implementation for vectorization
opportunities and possible coding style changes to allow for
auto-vector.




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