Re: [RFC v2] mac80211: implement eBDP algorithm to fight bufferbloat

[Jim Gettys <jg@freedesktop.org>]

On 02/19/2011 07:37 PM, Nathaniel Smith wrote:
> Actually, a few more comments just occurred to me...
>
> On Fri, Feb 18, 2011 at 1:21 PM, John W. Linville
> <linville@tuxdriver.com>  wrote:
>> Johannes' comment about tx status reporting being unreliable (and what
>> he was really saying) finally sunk-in.  So, this version uses
>> skb->destructor to track in-flight fragments.  That should handle
>> fragments that get silently dropped in the driver for whatever reason
>> without leaking queue capacity.  Correct me if I'm wrong!
>
> Should we be somehow filtering out and ignoring the packets that get
> dropped, when we're calculating the average packet transmission rate?
> Presumably they're getting dropped almost instantly, so they don't
> really take up queue space and they have abnormally fast transmission
> times, which will tend to cause us to overestimate max_enqueued? They
> should be rare, though, at least. (And presumably we *should* include
> packets that get dropped because their retry timer ran out, since they
> were sitting in the queue for that long.) Possibly we should just
> ignore any packet that was handled in less than, oh, say, a few
> microseconds?

I will note that AQM algorithms that are likely to work will need to 
know the actual "goodput" of the link. (This from talking to Van 
Jacobson about the problem we face.)

			- Jim