Yes, we share tags among all queues, but we generate the tag - known as IPTT
- in the LLDD now, as we can no longer use the request tag (as it is not
unique per all queues):
https://github.com/hisilicon/kernel-dev/commit/087b95af374be6965583c1673032fb33bc8127e8#diff-f5d8fff19bc539a7387af5230d4e5771R188
As I said, the branch is messy and I did have to fix 087b95af374.
Firstly this way may waste lots of memory, especially the queue depth is
big, such as, hisilicon V3's queue depth is 4096.
Secondly, you have to deal with queue busy efficiently and correctly,
for example, your real hw tags(IPTT) can be used up easily, and how
will you handle these dispatched request?
I have not seen scenario of exhausted IPTT. And IPTT count is same as
SCSI host.can_queue, so SCSI midlayer should ensure that this does not
occur.
Finally, you have to evaluate the performance effect, this is highly
related with how to deal with out-of-IPTT.
Some figures from our previous testing:
Managed interrupt without exposing multiple queues: 3M IOPs
Managed interrupt with exposing multiple queues: 2.6M IOPs
No managed interrupts: 500K IOPs.
Now my problem is that I hear some people are relying on the 3M
performance, even though it is experimental and unsafe. I need to follow
up on this. I really don't want to keep that code.
I'd suggest you to fix the stuff and post them out for review.
OK, I'll also check on adding that WARN you provided.
Thanks again,
John
Thanks,
Ming
.
