more network performance info: ether_output()

George Neville-Neil gnn at
Tue May 1 14:27:41 UTC 2012

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.


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