mbox series

[SRU,X/aws,0/1] aws: revert change to support instance types > 255 cpu cores

Message ID 20210223163607.76266-1-andrea.righi@canonical.com
Headers show
Series aws: revert change to support instance types > 255 cpu cores | expand

Message

Andrea Righi Feb. 23, 2021, 4:36 p.m. UTC 
BugLink: https://bugs.launchpad.net/bugs/1913739

[Impact]

The following commit was required to properly detect the right amount of
cores in large instance types (with > 255 cpus):

 561ef22a7d396289a1c5a1d18057ccdf9bb59826 "iommu/vt-d: Gracefully handle DMAR units with no supported address widths"

However, this patch seems to work correctly only with kernels > 4.4.
Considering the imminent EOL for this kernel it probably makes sense to
drop this patch for now, to prevent potential regressions.

[Test case]

Tests performed in the AWS cloud, the test case simply consists of
checking the amount of available cpus (running `nproc`).

[Fix]

Revert commit 561ef22a7d396289a1c5a1d18057ccdf9bb59826.

[Regression potential]

This change reverts a previously applied fix (that doesn't actually fix
the problem), so the only downside is simply that not all the available
cores will be detected on the large instance types (basically we are
simply reverting to an old behavior).

Comments

Andrea Righi March 11, 2021, 8 a.m. UTC | #1 
Will send a new patch soon, creating a new bug instead of re-using the
old one.

-Andrea

On Tue, Feb 23, 2021 at 05:36:06PM +0100, Andrea Righi wrote:
> BugLink: https://bugs.launchpad.net/bugs/1913739
> 
> [Impact]
> 
> The following commit was required to properly detect the right amount of
> cores in large instance types (with > 255 cpus):
> 
>  561ef22a7d396289a1c5a1d18057ccdf9bb59826 "iommu/vt-d: Gracefully handle DMAR units with no supported address widths"
> 
> However, this patch seems to work correctly only with kernels > 4.4.
> Considering the imminent EOL for this kernel it probably makes sense to
> drop this patch for now, to prevent potential regressions.
> 
> [Test case]
> 
> Tests performed in the AWS cloud, the test case simply consists of
> checking the amount of available cpus (running `nproc`).
> 
> [Fix]
> 
> Revert commit 561ef22a7d396289a1c5a1d18057ccdf9bb59826.
> 
> [Regression potential]
> 
> This change reverts a previously applied fix (that doesn't actually fix
> the problem), so the only downside is simply that not all the available
> cores will be detected on the large instance types (basically we are
> simply reverting to an old behavior).