34e0a279a9
Commit 26fed4ac4eab ("block: flush plug based on hardware and software
queue order") changed flushing of plug list to submit requests one
device at a time. However while doing that it also started using
list_add_tail() instead of list_add() used previously thus effectively
submitting requests in reverse order. Also when forming a rq_list with
remaining requests (in case two or more devices are used), we
effectively reverse the ordering of the plug list for each device we
process. Submitting requests in reverse order has negative impact on
performance for rotational disks (when BFQ is not in use). We observe
10-25% regression in random 4k write throughput, as well as ~20%
regression in MariaDB OLTP benchmark on rotational storage on btrfs
filesystem.
Fix the problem by preserving ordering of the plug list when inserting
requests into the queuelist as well as by appending to requeue_list
instead of prepending to it.
Fixes: 26fed4ac4eab ("block: flush plug based on hardware and software queue order")
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20230313093002.11756-1-jack@suse.cz
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.