Date: Fri, 18 Apr 2014 15:57:46 +0100 From: "seanrees@gmail.com" <seanrees@gmail.com> To: freebsd-xen@freebsd.org Subject: VM in Xen 4.1; poor packet forwarding performance on xn0 Message-ID: <CAJGy1F0%2BG1zq9hVbifTM2Vq6HHEmCM9hnFvQ=4t-4d5x=npaCA@mail.gmail.com>
next in thread | raw e-mail | index | archive | help
Hi there freebsd-xen, I tried first on freebsd-questions@ without success, so I thought to retry here. I run OpenVPN on a FreeBSD 10.0-Rp1 VM in Xen 4.1 (HVM). I am experiencing slow network performance on xn0 that seems to have developed after I upgraded to FreeBSD 10 (no other changes). I can only achieve about 0.5mbps through this interface when forwarding packets; packets in a single direction are fine (e.g; downloading to the VPS or pushing from the VPS) and clock in at many (>10 usually) mbps. Interestingly, my identical VM (configuration managed centrally) running on Xen 3.4 (HVM) does *not* have this issue. I did a little debugging and here's what I've noticed: - Not related to OpenVPN, repro'd using ssh -d. - Slow VM has a very low rate of context switches (~250) while forwarding, fast VM has a lot more (~2000) sampled over 5 seconds using systat -v. - I can't repro a context switch limit (tried a limited fork() bomb). - Tried with *and* without LRO and TSO on xn0 (and all combinations of LRO and TSO on/off) I started digging into the Xen drivers but I realised I am not equipped to debug this. I'm looking for suggestions on what to check. My provider is offering to move me to an older Xen host but I'd like to see if I can help identify a bug either in my configuration or perhaps in FreeBSD's Xen code. Sean
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?CAJGy1F0%2BG1zq9hVbifTM2Vq6HHEmCM9hnFvQ=4t-4d5x=npaCA>