[OpenAFS] performance and udp buffers

Simon Wilkinson sxw@your-file-system.com
Mon, 19 Nov 2012 09:18:19 +0000

On 19 Nov 2012, at 07:15, Jakub Moscicki wrote:
> Thanks for this analysis. The increased UDP works pretty well for us =
at CERN so far - albeit one limit gone other limits appear more =

I'm interested in what other limits you are hitting. I'm very aware of =
the problems with the listener thread load and scheduling, are you =
hitting any other problems with RX, or are they fileserver limitations?

>> management packets. 16Mbytes should be plenty providing that you =
>> d) Have a large number of 1.6.0 clients on your network
> Do you mean 1.6.0 (referring to a specific bug in 1.6.0) or 1.6.x =
(referring to some general change in client behaviour in 1.6 series)?=20

Specificaly 1.6.0, and prereleases. There is a truly unfortunate bug in =
those clients which causes them to create a gradually escalating ping =
flood against every fileserver they contact. At its worst, this creates =
a distributed denial of service attack against your fileservers. In =
terms of this discussion, the large number of incoming RX version =
packets can overwhelm the listener thread. As these packets are not flow =
controlled, they can force "real" data packets out of the UDP buffer. =
One solution to this problem is to drop these packets at the kernel =
firewall - you want to drop all version packets with an RX epoch of 999.