Re: performance of jailed processes

Hi there,

and I thought I was using jails on a 'big' scale... 400 jails on one 
single box, that's pretty amazing! What kind of jails are these, i.e. 
what are they used for? Encapsulating single processes/tasks only, or 
more complex things too? And what hardware are you on, CPU and memory-wise?

/Eirik

Dag-Erling Smørgrav wrote:
> Robert Watson <rwatson_at_freebsd.org> writes:
> 
>>- DNS -- I know you mentioned it, but I'd check anyway.  Especially if
>>  resolv.conf has bad DNS servers in it in the jails, etc.  You might try
>>  writing a trivial gethostbyname() test app and timing it in and out of
>>  the jail.  Also look at the reverse lookup done by the MySQL server.
>>  The impact of the source IP address might be particularly interesting.
> 
> 
> Packet traces already show that there is no delay between query and
> reply, the reply just takes a long time to transmit.
> 
> 
>>- It would be interesting to know if applications outside the jail bound
>>  to various IP addresses see performance differences depending on the IP
>>  used.  We have hashed IP address lookup, but there are some operations
>>  in the stack that require walking the list of addresses, etc.  If the
>>  non-jailed software always uses the first address because they're all in
>>  the same subnet, that might conceivably make a difference.  Taking jail
>>  out of the picture in some basic micro-benchmarks might help here also. 
> 
> 
> Non-jailed software always uses the first IP address, which is in its
> own subnet.  The jails draw from a pool of ~1000 IP addresses on the
> same interface, but in a different subnet.  The jail I've been testing
> in is about a quarter of the way down the list.
> 
> 
>>Can you identify any micro-benchmarks rather than macro-benchmarks that
>>reflect a significant difference?
> 
> 
> haven't had much luck with that...  fetch, for instance, doesn't seem
> to suffer, but with mysql the difference is dramatic:
> 
> (outside jail)
> 1 row in set (0.01 sec)
> 
> (inside jail)
> 1 row in set (13.20 sec)
> 
> note that 13 seconds is far too short for a DNS issue, and that the
> time reported is measured *after* login (i.e. after any DNS lookup)
> 
> DES