Starvation by diskd

[Brett Glass <squid-users@xxxxxxxxxxxxxx>]

I'm working with a FreeBSD-based gateway machine which is serving 
as a NAT router, recursive DNS resolver, and VPN server. It's also 
running Squid as a transparent proxy.

The system was seeing frequent dropped VPN connections, especially 
under heavy network loads.

After looking the system over and trying a few experiments, it 
looks to me as if VPN tasks (pptpd and ppp) and other networking 
tasks are being starved for CPU cycles by diskd. It may also be 
affecting natd (FreeBSD's NAT daemon, which runs in userland at 
standard priority) and named.

I've niced Squid down by 1 (to 1 below the standard priority, so 
that it has lower priority than natd or named) and have niced diskd 
down to standard priority, and the disconnections have stopped. I 
haven't changed the priority of unlinkd yet, but am thinking that 
it might be best to change it to one level above standard priority.

Are there "knobs" in squid.conf to control the priorities at which 
Squid, diskd, and unlinkd run? Shouldn't there be? And given that 
diskd apparently polls for I/O completion on many systems, 
shouldn't it have a lower default priority?

--Brett Glass