Re: [PATCH] block: do not reverse request order when flushing plug list

[Jens Axboe <axboe@kernel.dk>]

On Mon, 13 Mar 2023 10:30:02 +0100, Jan Kara wrote:
> 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.
> 
> [...]

Applied, thanks!

[1/1] block: do not reverse request order when flushing plug list
      commit: 34e0a279a993debaff03158fc2fbf6a00c093643

Best regards,
-- 
Jens Axboe