** Changed in: linux (Ubuntu)
Status: Confirmed => Fix Committed
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https://bugs.launchpad.net/bugs/1801305
Title:
Restore request-based mode to xen-blkfront for AWS kernels
Status in linux package in Ubuntu:
Fix Committed
Bug description:
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 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).
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