On 2/12/25 23:46, Caleb Sander Mateos wrote:
On Wed, Feb 12, 2025 at 3:21 PM Keith Busch <kbusch@xxxxxxxxxx> wrote:
On Wed, Feb 12, 2025 at 03:07:30PM -0800, Caleb Sander Mateos wrote:
Yes, we completely agree. We are working on incorporating Keith's
patchset now. It looks like there is still an open question about
whether userspace will need to enforce ordering between the requests
(either using linked operations or waiting for completions before
submitting the subsequent operations).
In its current form, my series depends on you *not* using linked
requests. I didn't think it would be a problem as it follows an existing
pattern from the IORING_OP_FILES_UPDATE operation. That has to complete
in its entirety before prepping any subsequent commands that reference
the index, and using links would get the wrong results.
As implementers of a ublk server, we would also prefer the current
interface in your patch series! Having to explicitly order the
requests would definitely make the interface more cumbersome and
probably less performant. I was just saying that Ming and Pavel had
raised some concerns about guaranteeing the order in which io_uring
issues SQEs. IORING_OP_FILES_UPDATE is a good analogy. Do we have any
examples of how applications use it? Are they waiting for a
completion, linking it, or relying on io_uring to issue it
synchronously?
With files you either handle it in user space by waiting for
completion or link them. The difference with buffers is that
linking wouldn't currently work for buffers, but we can change
that.
--
Pavel Begunkov
