b2k13 hackathon report: Henning Brauer (henning@) on Lazy IP Checksumming
Contributed by weerd on Tue Nov 5 10:08:10 2013 (GMT)
from the the-sum-of-all-evil-packets dept.
Henning Brauer (henning@) just sent in his report from the b2k13 hackathon, but
there's also a short
interview with Henning over on ioexception.de which you might
Berlin was a really convenient hackathon location for me, since
getting there from Hamburg feels like a little longer S-Bahn ride.
The fast ICE train makes it only a 90 minute trip. I arrived half a day
later than intended due to work interfering, but I quickly got going.
I foremost wanted to do some follow up work now that the big ckecksum
rewrite has matured a little bit. I wanted to remove the partial
pre-calculation of the protocol checksums in the template Protocol
Control Block (PCB) and the freshly inherited PCBs after accept. Doing
so was easier and faster than expected. I spent an hour or two only on
writing the diff, and about 2 days of convincing myself (by testing a
LOT and verifying code paths through inspection and, again, testing)
that it was actually right. I went on chasing a bug Stuart Henderson
(sthen@) was seeing. I found 2 corner cases we didn't handle correctly
(one fixed, one super rare case fixed in my tree but still to be
committed) -- but not sthen@'s bug. Lawrence Teo (lteo@) spotted that
one. I spent a lot of time with Alexander Bluhm (bluhm@) verifying logic
in corner cases. The cksum handling is complex and being able to sit
down together and think things through helped enormously. One more
reason why hackathons are so important for our development.
With the last round of changes committed, we wanted to head towards the
checksum handling being nicely contained in the
functions. This means the rest of the stack doesn't have to do anything
except to mark packets (or rather, pkthdr mbufs) as "needs
checksumming". We make pretty optimal use of hardware offloading
Aside from the work on the code it was really great to spend time with
the other developers again. We had a lot of fun and very productive
discussions in the hackroom, bars, and restaurants nearby. We also had
an awesome night in Kreuzberg and I got back at the hotel at 7:30am,
where they were just setting up for breakfast. Many thanks to everybody
involved, especially Uwe Stuehler (uwe@) and Stefan Sperling (stsp@). It
was a great little hackathon.
Thanks Henning for telling us about your efforts at the hackathon. We
usually try to blame getting back to the hotel at 7:30am on jetlag, but
in your case, no one would believe us.
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