On Tue, 2006-07-18 at 22:46 +0100, Andy Furniss wrote: > FWIW I think it may be possible to do it Patricks' way, as if I read it > properly he will end up with the ATM cell train length which gets > shifted by cell_log and looked up as before. The ATM length will be in > steps of 53 so with cell_log 3 or 4 I think there will be no collisions > - so special rate tables for ATM can still be made perfect.
Patrick is proposing that the packet lengths be sent to the kernel in a similar way to how transmission times (ie RTAB) is sent now. I agree that is how things should be done - but it doesn't have much to do with the ATM patch, other than he has allowed for ATM in the way he does the calculation in the kernel [1]. In particular: - As it stands, it doesn't help the qdiscs that use RTAB. So unless he proposes to remove RTAB entirely the ATM patch as it will still have to go in. - A bit of effort was put into making this current ATM patch both backwards and forwards compatible. Patricks patch would work with newer kernels, obviously. Older kernels, and in particular the kernel that Debian is Etch is likely to distribute would miss out. If Patrick did intend remove RTAB entirely then he needs to add a fair bit more into his patch. Since RTAB is just STAB scaled, its certainly possible. The kernel will have to do a shift and a division for each packet, which I assume is permissible. > As you say, I think mpu should be added aswell - so eth/other can benefit. Not really. The MPU is reflected in the STAB table, just as it is for RTAB. One other point - the optimisation Patrick proposes for STAB (over RTAB) was to make the number of entries variable. This seems like a good idea. However there is no such thing as a free lunch, and if you did indeed reduce the number of entries to 16 for Ethernet (as I think Patrick suggested), then each entry would cover 1500/16 = 93 different packet lengths. Ie, entry 0 would cover packet lengths 0..93, entry 1 94..186, and so on. A single entry can't be right for all those packet lengths, so again we are back to a average 30% error for typical VOIP length packets. - 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
