51a858817d
When replacing the Big Kernel Lock in commit 2a48fc0ab2 ("block:
autoconvert trivial BKL users to private mutex"), the lock was replaced
with a sr-wide lock.
This causes very poor performance when using multiple sr devices, as the sr
driver was not able to execute more than one command to one drive at any
given time, even when there were many CD drives available.
Replace the global mutex with per-sr-device mutex.
Someone tried this patch at the time, but it never made it upstream, due to
possible concerns with race conditions, but it's not clear the patch
actually caused those:
https://www.spinics.net/lists/linux-scsi/msg63706.html
https://www.spinics.net/lists/linux-scsi/msg63750.html
Also see
http://lists.xiph.org/pipermail/paranoia/2019-December/001647.html
Link: https://lore.kernel.org/r/20200218143918.30267-1-merlijn@archive.org
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Merlijn Wajer <merlijn@archive.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.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.