Benjamin Thery <[EMAIL PROTECTED]> writes: > Eric W. Biederman wrote:
>> A couple of random thoughts in trying to understand the numbers you are >> seeing. >> >> - Checksum offloading? >> >> You have noted that with the bridge netfilter support disabled you >> are still seeing additional checksum overhead. Just like you are >> seeing in the routing case. >> >> Is it possible the problem is simply that etun doesn't support >> checksum offloading, while your normal test hardware does? > > Looks like you are 100% correct. > I feel a bit stupid I didn't think about this "small" difference between real > NIC and etun. > > If I turn off checksum offloading on my physical NIC, the checksum "overhead" > (load) measured by oprofile is about the same in both case: when running > netperf > through a real NIC or through an etun tunnel first. Interesting. You can also 'enable' checksum offloading when using etun with ethtool. Which should just tell the kernel not to do checksumming. A bad idea in general but it might be useful in confirming where the performance overhead is coming from, and when used with routing I believe it is safe. When used with bridging I don't know. Thinking about it the ideal situation is to preserve skb->ip_summed it if came from another device, instead of unconditionally setting it. I need to take a good hard look at etun_xmit and make certain we are dotting all of the i's and crossing all of the t's for best performance and compatibility with the rest of the network stack. Eric - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
