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

Stefan Bader stefan.bader at
Tue Nov 6 12:31:58 UTC 2018

On 02.11.18 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(-)
Acked-by: Stefan Bader <stefan.bader at>

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