Re: libpcap capture performance drop

[Rick Jones <rick.jones2 () hp com>]

On Fri, 2011-05-27 at 10:39 -0700, Guy Harris wrote:
> On May 27, 2011, at 10:16 AM, Rick Jones wrote:
>
> > Is this new libpcap going to be guaranteed that the underlying NIC HW
> > isn't doing Large Receive Offload, or that the tracepoint in the stack
> > is below any stack's attempt to do Generic Receive Offload?
>
> If
>
>       1) your kernel supports the ethtool ioctls and libpcap was built with headers that support those ioctls
>
> and
>
>       2) the code below (which I checked in a few days ago) can detect all the forms of offloading that could cause 
> large "packets" to be delivered
>
> then, yes, the new libpcap will not trust the MTU value if any of the forms of offloading are enabled.  (It also 
> checks for TCP segmentation offloading and UDP fragmentation offloading, so that large *transmitted* "packets" won't 
> cause a problem.)

Excellent!  And that makes me wonder if I should add similar offload
checking (and reporting) code to netperf for its omni tests...

rick jones


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