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

[Giovanni Trematerra]

On Oct 12, 2009, at 10:45 AM, Thomas Backman wrote:
>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.

>How to reproduce/test:
>1) time file /etc/* > /dev/null a few times, or something similar that
>uses the disk; write down a common/average/median/whatever time.
>2) cat /dev/zero > /uncompressed_fs/filename # please make *sure* it's
>uncompressed, since ZFS with lzjb/gzip enabled will squish this into a
>kilobyte-sized file, thus creating virtually *no* IO.
>3) When cat has been running say 10 seconds, re-time command #1 and do
>some interactive stuff - run commands, edit files, etc.

Hi Thomas,
I'm trying to reproduce the issue though I don't have any ZFS filesystems.
I'm not using SSH neither serial console.
My system is quite responsive. I'm using a VmWare system with 2 cpu
support, 1MB RAM with
FreeBSD 7.2-RELEASE.
I don't know if the issue is related to ZFS or your hardware
configuration but can you report
what top(1) say during the slowdown?

--
Giovanni Trematerra