On Thu, Dec 06, 2007 at 03:49:51PM -0600, Chris Friesen wrote:
quoted text
> Andi Kleen wrote:
> >>Latency was very 
> >>important, so we ended up doing essentially a multicast unix socket 
> >>rather than taking the extra penalty for UDP multicast.
> >
> >
> >What extra penalty? Local UDP shouldn't be much more expensive than Unix.
> 
> On a 1.4GHz P4 I measured a 44% increase in latency between a unix 
> datagram and a UDP datagram.

That's weird.

quoted text
> 
> For UDP it has to go down the udp stack, then the ip stack, then through 

UDP doesn't really have much stack. IP is also very little assuming
cached route (connect called first) 

I would expect the copies to dominate in both cases.

-Andi
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