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Re: [PATCH] PowerPC: removed branch prediction from rint implementation
On Sun, Mar 31, 2013 at 8:02 PM, Adhemerval Zanella
<azanella@linux.vnet.ibm.com> wrote:
> This patch removes the branch prediction instructions for PowerPC rint
> implementation, replacing them for normal instructions. These instructions
> are actually hurting performance, it is safer and generally better to let
> the hardware handle it.
This is true on Power7. I believe it was not the case on older hardware.
> I added a rint benchmark test on benchtest framework. The results on a POWER7
> 64 bits are:
>
> MASTER: rint: ITERS:1e+09: TOTAL:12.0901s, MAX:48.908ns, MIN:5.312ns, 8.27124e+07 iter/s
> PATCH: rint: ITERS:1e+09: TOTAL:5.29302s, MAX:37.826ns, MIN:3.922ns, 1.88928e+08 iter/s
>
> Any tips, comments, advices?
We could conditionally exclude the branch hints on power7 and later
hardware as an alternative.
Steve?
Ryan