Messages in this thread | | | Subject | Re: [BK PATCHES] add ata scsi driver | From | James Bottomley <> | Date | 26 May 2003 14:47:08 -0400 |
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On Mon, 2003-05-26 at 14:18, Jens Axboe wrote: > > 1. Unified SG segment allocation. The SCSI layer currently has a > > mempool implementation to cope with this, is there a reason it can't > > become block generic? > > Of course that is doable, when I killed scsi_dma.c it was just a direct > replacement. Given that IDE had no such dynamic sg list allocation > requirements, it stayed in SCSI. Overdesign is never good :)
I agree with the sentiment. I just don't think variable size SG tables will remain the exclusive province of SCSI forever.
> > b. the host adapter is out of resources for *all* its devices. Block > > all device queues until we free some resources (again, usually a > > returning command). > > This is harder, because it involves more than one specific queue.
Yes, this is our nastycase, especially for locking and ref counting...you didn't say I only had to hand off the easy problems, though...
Hotpluggin has to have some awareness of this locality too. Even for IDE, hot unplug a card and you can lose two devices per cable.
> > 5. There needs to be some amalgam of the SCSI code for dynamic tag > > command queue depth handling. > > Again, block layer queueing was designed for what I needed (ide tcq) and > no overdesign was attempted. If you describe what you need, I'd be very > happy to oblige and add those bits. Some decent depth change handling, I > presume?
Pretty much yes, now. We lost all of our memory allocation nightmare problems when we moved away from fixed command queues per device to lazy command allocation using slabs.
James
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