Re: Lossy cogent p2p experiences?

[Saku Ytti <saku () ytti fi>]

On Sat, 9 Sept 2023 at 21:36, Benny Lyne Amorsen
<benny+usenet () amorsen dk> wrote:

> The Linux TCP stack does not immediately start backing off when it
> encounters packet reordering. In the server world, packet-based
> round-robin is a fairly common interface bonding strategy, with the
> accompanying reordering, and generally it performs great.

If you have
Linux - 1RU cat-or-such - Router - Internet

Mostly round-robin between Linux-1RU is gonna work, because it
satisfies the a) non congested b) equal rtt c) non-distributed (single
pipeline ASIC switch, honoring ingress order on egress),
requirements. But it is quite a special case, and of course there is
only a round-robin on one link in one direction.

Between 3.6-4.4 all multipath in Linux was broken, and I still to this
day help people with problems on multipath complaining it doesn't
perform (in LAN!).

3.6 introduced FIB to replace flow-cache, and made multipath essentially random
4.4 replaced random with hash

When I ask them 'do you see reordering', people mostly reply 'no',
because they look at PCAP and it doesn't look important to the human
observer, it is such an insignificant amount.. Invariable problem goes
away with hashing. (netstat -s is better than intuition on PCAP).


-- 
  ++ytti