more network performance info: ether_output()

[George Neville-Neil]

On Apr 20, 2012, at 15:03 , Luigi Rizzo wrote:

> Continuing my profiling on network performance, another place
> were we waste a lot of time is if_ethersubr.c::ether_output()
> 
> In particular, from the beginning of ether_output() to the
> final call to ether_output_frame() the code takes slightly
> more than 210ns on my i7-870 CPU running at 2.93 GHz + TurboBoost.
> In particular:
> 
> - the route does not have a MAC address (lle) attached, which causes
>  arpresolve() to be called all the times. This consumes about 100ns.
>  It happens also with locally sourced TCP.
>  Using the flowtable cuts this time down to about 30-40ns
> 
> - another 100ns is spend to copy the MAC header into the mbuf,
>  and then check whether a local copy should be looped back.
>  Unfortunately the code here is a bit convoluted so the
>  header fields are copied twice, and using memcpy on the
>  individual pieces.
> 
> Note that all the above happens not just with my udp flooding
> tests, but also with regular TCP traffic.

Hi Luigi,

I'm really glad you're working on this.  I may have missed this in a thread
but are you tracking these somewhere so we can pick them up and fix them?

Also, how are you doing the measurements.

Sorry, if these have been answered before.

Best,
George