Re: [Cake] openwrt build with latest cake and other qdiscs

[Sebastian Moeller <moeller0@gmx.de>]

Hi Jonathan,


On May 14, 2015, at 15:12 , Jonathan Morton <chromatix99@gmail.com> wrote:

> 
>> On 14 May, 2015, at 13:58, Sebastian Moeller <moeller0@gmx.de> wrote:
>> 
>>> Peeling is on the agenda; that’ll make sure we are dealing with actual, individual packets when we need to.  
>> 
>> I agree, that sounds conceptually much cleaner, but peeling is going to be costlier than pushing the segmentation to the NIC, so bandwidth aficionados will not appreciate unconditional peeling, I would guess.
>> 
>>> Certainly when dealing with cell-framing overhead, we *always* need to know individual packet sizes.
>> 
>> Well that or the sum for an aggregate as long as the sum takes all fancy “celling” into account, all we really need to know to how many bits the data expands on the wire.
> 
> Since GRO and GSO are for Ethernet and thus *don’t* take cell-framing overhead into account, I really do have to break them up for that purpose if no other.

	I am probably daft, but looking at the comment in front of skb_gso_network_seglen() (see http://lxr.free-electrons.com/ident?i=skb_gso_network_seglen ) makes me thick there is a way of getting the lengths of the individual segments of a GSO aggregate, and I assume one just adds the overhead to each and does the atm cell adjustments if need be, no need to touch the actual data or actually peel the geo. Then again I have not really followed the code and could easily be out to lunch. But sure peeling will be better fairness wise.

> 
> But beyond that, it can be conditional.  I propose that peeling be done if either:
> 
> 1) the ATM flag is set, or
> 
> 2) the aggregate would occupy more than 1ms on the wire (at the shaped rate).

	Oh, I like where you going with this a lot!

> 
> This would imply that pairs of 1500-byte packets would be separated at shaping rates up to 24Mbps, but smaller aggregates of smaller packets could still pass unhindered.  Conveniently, 24Mbps is also the ADSL cap, although since that’s the downstream rate, it’s not quite so relevant.

	Upstream the limit is more like 2.8Mbps (for AnnexJ)

> 
> Incidentally, GSO also interferes with my proposed ELR signalling, in a way that it doesn’t with ordinary ECN.  ELR needs to consider packets individually in order to apply the correct signalling pattern to them.  However, if the NIC did the signalling, that wouldn’t be an objection.

	Interesting thoughts.

Best Regards
	Sebastian

> 
> - Jonathan Morton
>