[SRU cosmic-aws][PATCH 0/6] LP: #1801305: xen-blkfront: restore request mode

[Kleber Souza]

On 11/02/18 09:57, Daniel Axtens wrote:
> In current Ubuntu kernels, PV blkfront drivers have blk-mq enabled by
> default and cannot use the old I/O scheduler.
>
> [Impact]
> blk-mq is not as fast as the old request-based scheduler for some
> workloads on HDD disks.
>
> [Fix]
> Amazon Linux has a commit which reintroduces the request-based
> mode. It disables blk-mq by default but allows it to be switched back
> on with a kernel parameter.
>
> For X this needs a small patch from upstream for error handling.
>
> For B/C this patchset is bigger as it includes the suspend/resume
> patches already in X, and a new fixup. These are desirable as the
> request mode patch assumes their presence.
>
> [Regression Potential]
> Could potentially break xen based disks on AWS.
>
> For B/C, the patches also add some code to the xen core around suspend
> and resume, this code is much smaller and also mirrors code already in
> Xenial.
>
> [Tests]
> Tested by AWS for Xenial, and their kernel engineers vetted the Xenial
> patches. I tested the Bionic and Cosmic patchsets with fio, the system
> appears stable and the IOPS promised for EBS Provisioned IOPS disks
> were met in my testing. I did an apt update/upgrade and everything
> worked (no hash-sum mismatches).
>
> Anchal Agarwal (1):
>   xen-blkfront: Fixed blkfront_restore to remove a call to negotiate_mq
>
> Munehisa Kamata (5):
>   xen/manage: keep track of the on-going suspend mode
>   xen/manage: introduce helper function to know the on-going suspend
>     mode
>   xenbus: add freeze/thaw/restore callbacks support
>   xen-blkfront: add callbacks for PM suspend and hibernation
>   xen-blkfront: resurrect request-based mode
>
>  drivers/block/xen-blkfront.c      | 475 ++++++++++++++++++++++++++----
>  drivers/xen/manage.c              |  73 +++++
>  drivers/xen/xenbus/xenbus_probe.c | 102 ++++++-
>  include/xen/xen-ops.h             |   4 +
>  include/xen/xenbus.h              |   3 +
>  5 files changed, 576 insertions(+), 81 deletions(-)
>
Hi Daniel,

The patches come from "AWS 4.14 kernel SRPM", does it mean they were
never upstream? If that's the case we need to mark the patches as SAUCE
(we could do it when applying them).


Thanks,

Kleber