Freebsd IP Forwarding performance (question, and some info) [7-stable, current, em, smp]

[Julian Elischer]

Artem Belevich wrote:
>>  Prefetching when you are waiting for the data isn't a help.
> 
> Agreed. Got to start prefetch around <put your memory latency here>ns
> before you actually need the data and move on doing other things that
> do not depend on the data you've just started prefetching.
> 
>>  what you need is a speculative prefetch where you an tell teh processor "We
>> will probably need the following address so start getting it while we go do
>> other stuff".
> 
> It does not have to be 'speculative' either. 

"*Will*" is just a very definite subset of 'speculation' :-)

> In this particular case
> we have very good idea that we *will* need some data from ethernet
> header and, probably, IP and TCP headers as well. We might as well tel
> the hardware to start pulling data in without stalling the CPU. Intel
> has instructions specifically for this purpose. I assume AMD has them
> too.
> 
> --Artem
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