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Now that we have multishot poll requests, one SQE can emit multiple
CQEs. given below example:
sqe0(multishot poll)-->sqe1-->sqe2(drain req)
sqe2 is designed to issue after sqe0 and sqe1 completed, but since sqe0
is a multishot poll request, sqe2 may be issued after sqe0's event
triggered twice before sqe1 completed. This isn't what users leverage
drain requests for.
Here the solution is to wait for multishot poll requests fully
completed.
To achieve this, we should reconsider the req_need_defer equation, the
original one is:
all_sqes(excluding dropped ones) == all_cqes(including dropped ones)
This means we issue a drain request when all the previous submitted
SQEs have generated their CQEs.
Now we should consider multishot requests, we deduct all the multishot
CQEs except the cancellation one, In this way a multishot poll request
behave like a normal request, so:
all_sqes == all_cqes - multishot_cqes(except cancellations)
Here we introduce cq_extra for it.
Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
Link: https://lore.kernel.org/r/1618298439-136286-1-git-send-email-haoxu@linux.alibaba.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.