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Support bio polling (REQ_POLLED) in the following approach: 1) only support io polling on normal READ/WRITE, and other abnormal IOs still fallback to IRQ mode, so the target io (and DM's clone bio) is exactly inside the dm io. 2) hold one refcnt on io->io_count after submitting this dm bio with REQ_POLLED 3) support dm native bio splitting, any dm io instance associated with current bio will be added into one list which head is bio->bi_private which will be recovered before ending this bio 4) implement .poll_bio() callback, call bio_poll() on the single target bio inside the dm io which is retrieved via bio->bi_bio_drv_data; call dm_io_dec_pending() after the target io is done in .poll_bio() 5) enable QUEUE_FLAG_POLL if all underlying queues enable QUEUE_FLAG_POLL, which is based on Jeffle's previous patch. These changes are good for a 30-35% IOPS improvement for polled IO. For detailed test results please see (Jens, thanks for testing!): https://listman.redhat.com/archives/dm-devel/2022-March/049868.html or https://marc.info/?l=linux-block&m=164684246214700&w=2 Tested-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
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.