Re: PATCH [5/15] qla2xxx: SG tablesize update

[Jeff Garzik <jgarzik@pobox.com>]

James Bottomley wrote:
> On Sun, 2004-03-14 at 15:36, Jeff Garzik wrote:
> 
>>On Sun, Mar 14, 2004 at 09:59:55AM -0500, James Bottomley wrote:
>>
>>>The Qla chips are rather weird in that they have a single issue queue
>>>(whose size you can vary) but whose entry formats are fixed.  If I
>>>remember correctly, an initial command can have 4 SG elements, but a
>>>follow on entry can have 7 (not sure of the figures).  But anyway, large
>>>SG commands end up having to find multiple entries in this queue (and
>>>being a single issue queue for the entire card, it has to be mutexed
>>>while you search).  The more resources you need, the more difficult the
>>>search and the more contention you generate on the resource mutex.
>>
>>The block layer can handle this type of hardware just fine ;-)
>>
>>In my SATA hacking I am finding several devices that one must constrain
>>based on hardware-global resources, rather than just TCQ (or lack
>>thereof).
> 
> 
> I'm sorry, I must have missed the multiple queues down to a single HBA
> queue API in the block layer, which one is it again?

Not saying the block layer provides this capability, simply that it is 
possible in any block driver.  It required < 20 LOC in carmel.c to do 
this in a hardware-specific fashion, so it seemed unnecessary to invent 
a new API...  I would like to see something similar in cciss.c, in fact...

	Jeff