Extreme console latency during disk IO (8.0-RC1, previous releases also affected according to others)

[Ivan Voras]

Thomas Backman wrote:
> I'm copying this over from the freebsd-performance list, as I'm looking 
> for a few more opinions - not on the problems *I* am having, but rather 
> to check whether the problem is universal or not, and if not, find a 
> possible common factor.
> In other words: I want to hear about your experiences, *good or bad*!
> 
> Here's the original thread (not from the beginning, though): 
> http://lists.freebsd.org/pipermail/freebsd-performance/2009-October/003843.html 
> 
> 
> Long story short, my version: when the disk is stressed hard enough, 
> console IO becomes COMPLETELY unbearable. 10+ seconds to switch between 
> windows in screen(1), running (or even typing) simple commands, etc. 
> This happens both via SSH and the serial console.

Hmm, this looks familiar - I've noticed it before on the physical (VGA) 
console and I notice it all the time under VMWare. It sort of looks like 
disk IO really blocks network IO in this case - I use the VMs over ssh.