Re: [PATCH v7 04/17] tracing: add static function tracer support for MIPS

Maciej W. Rozycki
2009-11-11T13:15:04Z

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