Re: scsi: aic7xxx hang since v2.6.28-rc1 ...

[Ingo Molnar <mingo@elte.hu>]

* Mike Anderson <andmike@linux.vnet.ibm.com> wrote:

> Ingo Molnar <mingo@elte.hu> wrote:
> > 
> > * Alan Stern <stern@rowland.harvard.edu> wrote:
> > 
> > > I have no idea if this will make any difference for the 
> > > problem you're seeing, but it has been submitted and it's 
> > > worth trying out.  If the problem still occurs, I'll write a 
> > > diagnostic patch to add log messages giving the destiny of 
> > > each request in scsi_io_completion().
> > 
> > OK, i've undone the reverts and have applied your fix - it will 
> > take a few hours to see whether the hang still occurs.
> 
> I know already started your testing, but..

and that particular box already survived 20 test iterations in 
the past few hours - while it would hang after 5-10 iterations 
before. So i think Alan's fix is making a difference. I'll be 
able to tell for sure tomorrow morning.

> I find it informative to set my scsi logging to the value 
> below to display non-zero IO status on commands. The overhead 
> impact is low for good completions.
> 
> sysctl -w dev.scsi.logging_level=4100
> 
> Note: This does not provide the exact policy that 
> scsi_io_completion will take on the IO, but it provides the 
> input to scsi_io_completion which should help.

will do that next time around i have a bug like this. (or if 
this bug triggers again)

OTOH, the hang took quite a bit of IO to occur. Sometimes the 
box would be able to build a new kernel and reboot into it, 
without the hang.

	Ingo