ACK/cmnt: [SRU xenial-aws][PATCH 0/2] LP: #1801305: xen-blkfront: restore request mode

[Daniel Axtens]

Hi Kleber,

Good catch. Would you like me to resubmit the 3 series with this
fixed? If so, do I include the existing ACKs, or is there any tooling
that depends on the particular messages with the particular subjects
being in someone's inbox?

Regards,
Daniel
On Thu, Nov 8, 2018 at 4:24 AM Kleber Souza <kleber.souza at canonical.com> wrote:
>
> On 11/02/18 10:01, 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).
> >
> > Christoph Hellwig (1):
> >   xen-blkfront: don't use req->errors
> >
> > Munehisa Kamata (1):
> >   xen-blkfront: resurrect request-based mode
> >
> >  drivers/block/xen-blkfront.c | 333 +++++++++++++++++++++++++++++------
> >  1 file changed, 276 insertions(+), 57 deletions(-)
> >
> Patch 2/2 probably need a SAUCE tag since it doesn't seem to come
> from mainline.
>
> Acked-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>
>