Re: calling scsi_adjust_queue_depth() during I/O...

[James Bottomley <James.Bottomley@SteelEye.com>]

On Sat, 2005-08-06 at 02:10 +0900, Tejun Heo wrote:
>  Yes, we can do that, but I'm not sure if that would be necessary.
> AFAIK, queues are normally not very deep and a tag only occupies one
> pointer and one bit.  Also, the shrinking operation isn't very common,
> at least for traditional SPI devices and SATA drives, I think.
> 
>  Are newer SCSI devices (say, SAS/iSCSI) different? - like having very
> deep queue and needing dynamic queue depth adjustment?  If that's the
> case, I think I can implement shrinking in a separate patch. (and try
> not to screw up this time ;-)

Well, yes, there are reasons for wanting deeper queues, but I'd leave it
for the time being.

What I'm looking into is support for aic7xxx/aic79xx queueing.  There,
the sequencer has to have a globally unique tag (from which it generates
the device locally unique tag internally).  That gives TCQ depths of up
to 512 I believe.  However, still probably not a significant waste of
memory to worry about.

James