strange i/o and tty lockups/delays on 6.1, strange sync() issue

[Nate Eldredge]

On Wed, 31 Oct 2007, Marek Blaszkowski wrote:

> Hi,
> my config:
> thunder k8sr, dual opteron 244, 8GB RAM, FreeBSD 6.1, sata disk
>
>
> for time to time (every 10 or 20 secs) any process which try write or 
> read any, even small file, is locked for a couple seconds (about 7 or 9 
> secs), very iritating when I try save small files edited in vim (size 
> about 2-3 kbytes), it's looks like this: #vim /path/to/file ...editing..
> :w
> and now (afetr w command) vim freeze for 7-10 secs until it displays 
> "file written".
>
> Delays accours on tty, too. In vim I can't move around edited file 
> (up/down in rows), vim just got hang, strange is that I can switch 
> (durning vim lockup) beetwen virtual screen consoles.

[sync takes a long time too]

Is there anything in the log files?  This might happen if the disk access 
fails or times out; the kernel resets the controller and tries again, 
which takes a long time.  That would indicate that the disk is probably 
failing, in which case it should be backed up and replaced as soon as 
possible.  You could also see if smartctl reports anything significant.

If that's not it, you might try running top and see if any process 
accumulated CPU seconds during the hang.

I experienced a couple of other issues where things would hang 
momentarily.  One was fixed by disabling ACPI (it's a long story) and the 
other by enabling PREEMPTION.  So if the disk is okay those are two more 
things you could try.

Hope this helps.  I'd be interested to know what you find out.

-- 
Nate Eldredge
nge at cs.hmc.edu