On Wed, 11 Nov 2009, Wu Zhangjin wrote:
> > -mlong-calls really degrades performance. I have seen things like 6%
> > drop in network packet forwarding rates with -mlong-calls.
> >
>
> so much drop? seems only two instructions added for it: lui, addi. from
> this view point, I think the -fno-omit-frame-pointer(add, sd, move...)
> will also bring with much drop.
No, register jumps cannot be predicted -- this is where the performance
goes on any serious processor -- the two extra instructions are nothing
compared to that. OTOH frame pointer calculations are pure arithmetic, so
you only lose time incurred by the instructions themselves.
Maciej
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