Re: DP performance

[Marko Zec <zec@xxxxxxxx>]

On Thursday 01 December 2005 15:27, Danial Thom wrote:
> The issue is that RX is absolute, as you cannot
> "decide" to delay or selectively drop since you
> don't know whats coming. Better to have some
> latency than dropped packets.

No, if the system can't cope with the inbound traffic, it's much better 
to drop or flow-control the inbound packets early (in the hardware) 
then to waste other system resources (bus time, CPU cycles) on useless 
processing if the same packets will never be forwarded.  Giving 
absolute priority to RX processing leads to livelock at high traffic 
loads, a phenomenon which was well known and studied for at least a 
decade.

Cheers,

Marko


> But if you don't 
> dedicate to RX, then you have an unknown amount
> of cpu resources doing "other stuff". The
> capacity issues always first manifest themselves
> as rx overruns, and they always happen a lot
> sooner on MP machines than UP machines. The LINUX 
> camp made the mistake of not making RX important
> enough, and now their 2.6 kernels drop packets
> all over the ranch. But audio is nice and
> smooth...
>
> How to do it or why its difficult is a designer's
> issue. I've not yet been convinced that MP is
> something thats suitable for a network intensive
> environment as I've never seen an MP OS that has
> come close to Freebsd 4.x UP performance.
>
> DT
>
>
>
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