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

[Kris Kennaway]

Luigi Rizzo wrote:
> On Mon, Oct 12, 2009 at 09:48:42PM +0200, 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.
> 
> hi,
> this issue (not specific to FreeBSD, and not new -- it has been
> like this forever) is discussed in some detail here
> 
> 	http://www.bsdcan.org/2009/schedule/events/122.en.html
> 
> The following code (a bit outdated) can help
> 
> http://lists.freebsd.org/pipermail/freebsd-stable/2009-March/048704.html

Are you certain?  The reported symptoms sound very unusual.  Can you 
reproduce the problem with the provided instructions yourself?

Kris