CAM tags / reset problem

[Ade Lovett]

On Sep 17, 2005, at 00:13 , Scott Long wrote:
> It's a bit late tonight for me to think coherently about this and give
> the patch a good review, but I promise that it will happen.  Maybe
> Justin, Ken, Matt, or Nate can also step in and look at it.  Are  
> you saying that there are multiple bus resets happening in  
> relatively quick
> succession on each bus during the inital probe?  Are you observing  
> this
> with only a particular controller family, or with multiple ones?

This is fallout from the well-documented issues with multiple Seagate  
drives on an Adaptec 39320 controller:

ahd0: <Adaptec 39320A Ultra320 SCSI adapter> port 0x3400-0x34ff, 
0x3000-0x30ff me
m 0xfc200000-0xfc201fff irq 48 at device 1.0 on pci2
ahd0: [GIANT-LOCKED]
aic7902: Ultra320 Wide Channel A, SCSI Id=7, PCI-X 101-133Mhz, 512 SCBs


After the recent nswbuf patch, we were still noticing anomalies with  
performance on the chain.  This is certainly a degenerate case  
(Seagate drives on a U320 chain), but as far as I can tell it applies  
to any set of controller/disk pairs should multiple bus resets occur  
on startup.

I've got another test box with Hitachi drives (same controller) and  
am trying to figure out a way to engineer a set of events that would  
cause such multiple resets but have as yet been unsuccessful.

However, with this patch, we now have chains of 7/8 Seagate drives  
running at U320 with overall bus throughput around 312MBps.  Prior to  
this, on random read/writes, we were observing less than 100MBps.

It definitely merits looking at to see if it breaks anything  
elsewhere (particularly with "well-behaved" SCSI controller/disk  
combinations), hence the request for review.

-aDe