Re: IB_POLL_DIRECT

[Jason Gunthorpe <jgg@nvidia.com>]

On Tue, Jun 06, 2023 at 03:54:25PM -0500, Bob Pearson wrote:
> AFAIK the poll workqueue and poll softirq cqs are working correctly but the poll direct cq sometimes
> loses the thread and just stops processing those cqs. The test cases sometimes recover after about
> a 2 second delay and start processing again and eventually fail after about a 10 second delay and
> cleanup and go home.

This sort of sounds like a race with re-arming?
 
> The failures feel like a race or at least are timing sensitive. If you run the test suite several times
> various test cases will sometimes succeed and sometimes fail. But they always fail in the same way.
> 
> Looking at the mlxn drivers for inspiration, I don't see anything specific about IB_POLL_DIRECT except
> that they have a private version of send_queue_drain which also calls a cqe drain function which calls
> ib_process_cq_direct() in a loop until the cq is drained. But this is only during qp tear down. (No other
> verbs driver does this but as far as I know no other driver is passing blktests.) This is only done for
> IB_POLL_DIRECT, so I wonder, is this required to use that correctly?
> 
> I am still figuring out how IB_POLL_DIRECT works. It doesn't allow the driver to call cq->comp_handler so
> I don't know how it figures out when there are new wcs to process.

IIRC POLL_DIRECT means you don't get completion interrutps and instead
the ULP has to occasionally call ib_process_cq_direct() which will
pull out the CQEs.

So you should look at how ib_process_cq_direct() is being called in
srp and presumably something about that logic is not calling it..

It kind of looks like SRP is using it to reap send completions when
the send queue progresses, so maybe your issue is that the sendq is
getting stuck?

Jason