I'm running PPPoEoATM here. I don't know what my actual PPPoE overhead is, but I guess 10 bytes is reasonably close enough. PPPoE is handled by my Westell Wirespeed, which doesn't provide any useful cell information. At the moment I cannot easily obtain a cell count to determine my actual PPP overhead.
Try bumping the protocol_overhead up to 16 for PPPoE (from 10). You should also make sure that your MTU is lower than that required by your PPPoE provider or else you will get ethernet packet fragmentation and I doubt we want to extend the patch to cover those situations anyway.
The patch should actually have most benefit when you are doing transfers with smaller packets. I think with larger constant streams like the one you tested, there will be little difference between bumping up the interface speed with the patch or leaving it all as it was (at the end of the day we are mostly just shifting the calculation of interface speed somewhere else).
Perhaps I need to idle everything and do one of those 'speed tests' to see what my actual upstream is. Could be it's really around 224, since I'm not guaranteed 256 by my ISP anyway.
Your upstream will be 256Kbits of ATM bandwidth. This consists of 53 byte packets with 48 bytes of data. So you already only have 256 * 48/53 of real bandwidth. We then have to take off PPP headers and PPPoE headers.
We are obviously still a few bytes out with this patch or else you should be able to crank up the speed to 250 ish and still see your ping speeds stay low. I will investigate further
Ed W
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