ACK: [SRU][PULL v4][G/aws] config changes to improve hibernation on Xen instance types

[Kamal Mostafa]

LGTM.  Thanks for the smart and effective adjustments here, Andrea.

Acked-by: Kamal Mostafa <kamal at canonical.com>

 -Kamal

On Thu, Nov 05, 2020 at 07:05:48PM +0100, Andrea Righi wrote:
> BugLink: https://bugs.launchpad.net/bugs/1902926
> BugLink: https://bugs.launchpad.net/bugs/1732512
> BugLink: https://bugs.launchpad.net/bugs/1879711
> 
> [Impact]
> 
> The 5.8 kernel (groovy) is not still 100% reliable with hibernation,
> especially on the Xen instance type. However, re-aligning the config
> options as much as possible with the 5.4 kernel (focal) allows to
> hibernate and resume with a success rate close to 100% (according to our
> tests on the AWS cloud).
> 
> [Test case]
> 
>  - spin up an AWS instance (for example a c4.8xlarge instance type)
>  - run a memory stress test
>  - hibernate
>  - resume
>  - verify that the system has been resumed correctly and the memory
>    stress test is still running
> 
> [Fix]
> 
> The following fixes must be applied to improve hibernation/resume
> reliability:
> 
>  - disable CONFIG_SUSPEND (suspend to memory is not supported in AWS and
>    it can introduce a deadlock condition with the Xen hibernation layer)
>  - make sure CONFIG_DMA_CMA is disabled (this introduces another
>    deadlock condition with Xen)
>  - disable CONFIG_FB_HYPERV: this would enable CONFIG_DMA_CMA and we
>    don't want that (to prevent the Xen deadlock); moreover this driver
>    is not needed at all in the AWS environment
>  - disable CONFIG_XEN_FBDEV_FRONTEND: this is also not required in the
>    AWS environement and it has the potential of breaking hibernation
>  - disable CONFIG_INPUT_XEN_KBDDEV_FRONTEND
>  - disable CONFIG_XEN_BALLOON
>  - make sure xen-netfront is *not* compiled as a module, otherwise
>    it seems that the network is not properly resumed on the t2 instance
>    types (enforce that in the annotations file to prevent changing it
>    again in the future)
>  - remove all sound-related modules (not really needed in the AWS cloud,
>    they were also disabled on 5.4)
> 
> [Regression potential]
> 
> These are all .config changes. With these changes we are basically
> re-aligning with the previous 5.4 settings and we have experimentally
> verified (tests) that these changes are increasing the success rate of
> hibernation. So the regression potential is minimal.
> 
> Changes v3 -> v4:
>  - enforce xen-netfront to be statically compiled in the kernel
>    (otherwise the network is not properly resumed on the t2 instance types)
> 
> ----------------------------------------------------------------
> The following changes since commit f352dd559e7c0ab7aa8db3b91f698e4cbbfbcbe3:
> 
>   UBUNTU: Ubuntu-aws-5.8.0-1011.11 (2020-10-22 11:23:44 +0200)
> 
> are available in the Git repository at:
> 
>   git://git.launchpad.net/~arighi/ubuntu/+source/linux-aws/+git/groovy tags/aws-config-update
> 
> for you to fetch changes up to 6f973e789d4bec33c42a21dcbddf3a8a5596cb45:
> 
>   UBUNTU: [Config] [aws] remove all sound-related modules (2020-11-05 18:39:59 +0100)
> 
> ----------------------------------------------------------------
> Andrea Righi (7):
>       UBUNTU: [Config] [aws] make sure CONFIG_FB_HYPERV is disabled
>       UBUNTU: [Config] [aws] make sure CONFIG_SUSPEND is disabled
>       UBUNTU: [Config] [aws] disable CONFIG_XEN_FBDEV_FRONTEND
>       UBUNTU: [Config] [aws] disable CONFIG_INPUT_XEN_KBDDEV_FRONTEND
>       UBUNTU: [Config] [aws] disable CONFIG_XEN_BALLOON on amd64
>       UBUNTU: [Config] [aws] enforce CONFIG_XEN_NETDEV_FRONTEND
>       UBUNTU: [Config] [aws] remove all sound-related modules
> 
>  debian.aws/abi/5.8.0-1010.10/amd64/aws.modules | 478 -----------------
>  debian.aws/abi/5.8.0-1010.10/arm64/aws.modules | 479 -----------------
>  debian.aws/config/amd64/config.common.amd64    |   3 +-
>  debian.aws/config/annotations                  | 655 +----------------------
>  debian.aws/config/arm64/config.common.arm64    |   3 +-
>  debian.aws/config/config.common.ubuntu         | 693 +------------------------
>  debian.aws/control.d/aws.inclusion-list        |   1 -
>  7 files changed, 21 insertions(+), 2291 deletions(-)
> 
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