Bug#760324: linux 3.16 (jessie): Please backport virtio-scsi change queue depth (761f1193) from upstream
Source: linux
Version: 3.16
Severity: wishlist
Dear Maintainer,
Linux 3.17 will include commit 761f1193, 'virtio-scsi: Implement change_queue_depth for
virtscsi targets'; it would be great if this commit could be backported to the Debian
3.16 kernel (for jessie). Upstream link is:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=671f1193
This commit will allow users to manually change per-SCSI Target queue depths via sysfs.
It will also allow SCSI TASK SET FULL congestion events to scale down target queue depths
as needed.
The implementation of virtscsi_change_queue_depth is identical to implementations in
other SCSI LLDs, such as drivers/scsi/libiscsi.c:iscsi_change_queue_depth().
Testing:
I backported and tested this commit with the 3.16-rc6 kernel from the experimental suite.
First tested manually changing per-target queue depth via sysfs. It does not work without
the patch, does work with the patch applied.
I also tried manually sending SCSI BUSY / TASK SET FULL messages with an instrumented
disk, using Google Compute Engine's hypervisor. After an appropriate number of TASK
SET FULL messages (10), we see the number of inflight commands to a single SCSI target
reduced.
-- System Information:
Debian Release: 7.6
APT prefers stable-updates
APT policy: (500, 'stable-updates'), (500, 'testing'), (500, 'stable')
Architecture: amd64 (x86_64)
Kernel: Linux 3.14-0.bpo.2-amd64 (SMP w/16 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
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