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

[John W. Linville]

On Fri, Feb 18, 2011 at 07:44:30PM -0800, Nathaniel Smith wrote:
> On Fri, Feb 18, 2011 at 1:21 PM, John W. Linville
> <linville at tuxdriver.com> wrote:
> > +       /* grab timestamp info for buffer control estimates */
> > +       tserv = ktime_sub(ktime_get(), skb->tstamp);
> [...]
> > +               ewma_add(&sta->sdata->qdata[q].tserv_ns_avg,
> > +                        ktime_to_ns(tserv));
> 
> I think you're still measuring how long it takes one packet to get
> from the end of the queue to the beginning, rather than measuring how
> long it takes each packet to go out?

Yes, I am measuring how long the driver+device takes to release each
skb back to me (using that as a proxy for how long it takes to get
the fragment to the next hop).  Actually, FWIW I'm only measuring
that time for those skb's that result in a tx status report.

I tried to see how your measurement would be useful, but I just don't
see how the number of frames ahead of me in the queue is relevant to
the measured link latency?  I mean, I realize that having more packets
ahead of me in the queue is likely to increase the latency for this
frame, but I don't understand why I should use that information to
discount the measured latency...?

John
-- 
John W. Linville		Someday the world will need a hero, and you
linville at tuxdriver.com			might be all we have.  Be ready.