Re: NetBSD 5.1 TCP performance issue (lots of ACK)

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Mon, Oct 17, 2011 at 01:25:28PM -0400, Greg Troxel wrote:
> 
> To diagnose this, I recommend making a tcpdump of the traffic with
> 
> tcpdump -w TRACE tcp
> 
> and then using  tcpdump2plot in graphics/xplot-devel.
> 
> I am not clear if graphics/xplot-devel (or /xplot) has caught up to
> minor changes in NetBSD tcp

I looked at this quickly but I didn't understand how to use tcpdump2plot
(or maybe tcpdump2plot is too old for our tcpdump).

> 
> These plots are not 100% obvious how to read, but I'm happy to look at
> them if you can provide the above trace file.   Counts are useful, but
> this lets you see the fine-grained behavior of what got sent when.

ftp://ftp-asim.lip6.fr/outgoing/xen1.3.pcap

> 
> From the stats, it looks like there is loss in the data stream causing
> SACK.

I've noticed this. I don't know where the data loss occurs.
No errors on interfaces, and no drop in ipintr or interface queue.

> But I don't see how there would be 237850 pure acks for ~98K data
> packets; there should be more like 49K.

that's my understanding too. There's way too much ack. the trace for both the
linux and NetBSD clients where collected on the NetBSD server, so I don't
think it can be bogus duplicate packets at the capture level.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--