On Mon, Oct 21, 2019 at 12:49:53PM +0100, John Garry wrote: > > > > > > > > > > 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. That check isn't correct, and each hw queue should have allowed .can_queue in-flight requests. > > > > > 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 Then you see the performance regression. Thanks, Ming
