Tejun Heo, on 07/28/2010 06:44 PM wrote:
Hello,
On 07/28/2010 04:37 PM, James Bottomley wrote:
I don't remember all the details now but IIRC what was necessary was
earlier write failure failing all commands scheduled as ordered. Does
ACA / UA_INTLCK or whatever allow that?
No. That requires support for QErr ... which is in the same mode page.
I see.
The real reason we have difficulty is that BUSY/QUEUE_FULL can cause
reordering in the issue queue, which is a driver problem and not in the
SCSI standards.
Ah yeah right. ISTR discussions about this years ago. But one way or
the other, given the limited amount of ordering information available
under the block layer, I doubt the benefit of doing would be anything
significant. If it can be done w/o too much complexity, sure, but
otherwise...
Hmm, this thread was started from the need to avoid queue draining,
because it is a big performance hit. The use of ordered commands allows
to _completely_ eliminate queue draining _at all_. It looks to be a
significant benefit worth some additional complexity.
Vlad
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
