NACK: [SRU][PULL v2][G/aws] config changes to improve hibernation on Xen instance types

[Andrea Righi]

Superseded. Will send a v3 soon.

-Andrea

On Wed, Nov 04, 2020 at 04:33:39PM +0100, Andrea Righi wrote:
> BugLink: https://bugs.launchpad.net/bugs/1732512
> BugLink: https://bugs.launchpad.net/bugs/1879711
> 
> [Impact]
> 
> After moving to 5.8 the config for the AWS kernel has been re-generated
> starting from the generic 5.8 kernel. However, in the process, we missed
> some important config options that are required to properly support
> hibernation on Xen instance types.
> 
> Re-align the config starting from a 5.4 kernel and report explicitly in
> the annotations file the relevant config options required by
> hibernation.
> 
> These changes have been tested in the AWS environment using Xen and KVM
> instance types. Without these config changes hibernation is currently
> broken on certain instance types.
> 
> With these changes hibernation is still not 100% reliable, but they
> improve hibernation success rate a little bit with the 5.8 kernel.
> 
> More config changes will come in a future pull request (I'll create a
> separate bug for them).
> 
> [Test case]
> 
>  - start a Xen-based instance (i.e., c4.8xlarge)
>  - start a memory stress test on it
>  - hibernate & resume
>  - verify that the instance has been properly resumed and the memory
>    stress test is still running
> 
> [Fix]
> 
>  - 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
>    dont' 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
> 
> [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 v1 -> v2:
>  - apply only the config changes we know for sure that are required to
>    improve hibernation success rate
> 
> ----------------------------------------------------------------
> 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 bab427a64f957b5f33b3cb84c2da6d9da3817882:
> 
>   UBUNTU: [Config] [aws] disable CONFIG_XEN_FBDEV_FRONTEND (2020-11-04 15:59:00 +0100)
> 
> ----------------------------------------------------------------
> Andrea Righi (3):
>       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
> 
>  debian.aws/abi/5.8.0-1010.10/amd64/aws.modules |  2 --
>  debian.aws/abi/5.8.0-1010.10/arm64/aws.modules |  1 -
>  debian.aws/config/amd64/config.common.amd64    |  1 +
>  debian.aws/config/annotations                  | 11 +++++++----
>  debian.aws/config/arm64/config.common.arm64    |  1 +
>  debian.aws/config/config.common.ubuntu         |  5 ++---
>  6 files changed, 11 insertions(+), 10 deletions(-)