Bug#1028376: linux-image-5.10.0-20-amd64: PHP Performance on kernels above 5.10.0-16-amd64 on Debian 11

[Salvatore Bonaccorso <carnil@debian.org>]

Hi,

On Tue, Jan 10, 2023 at 10:00:51AM +0100, Tomeu Vidal Vázquez wrote:
> Package: src:linux
> Version: 5.10.158-2
> Severity: normal
> 
> Dear Maintainer,
> 
>    * What led up to the situation? After kernel 5.10.0-16-amd64 (5.10.0-17-amd64 and above) the performace of the machine is dropping. The same machine running kernel 5.10.0-16-amd64 has about 100% less of load.
> 
>    * What exactly did you do (or not do) that was effective (or ineffective)? Booting machine with kernel 5.10.0-16-amd64.
>    * What was the outcome of this action? Booting machine with kernel 5.10.0-16-amd64 solve the problem. Above kernels from 5.10.0-17-amd64 to 5.10.0-20-amd64 has 100% more load.
>    * What outcome did you expect instead? I expect the same performace between diferent kernels

The update bumping ABI to 17, 5.10.136-1, was the one introducing
mitigations for RETbleed on AMD (CVE-2022-29900) and Intel
(CVE-2022-29901) processors.

Have a look at
https://lore.kernel.org/all/PH0PR05MB8448A203A909959FAC754B7AAF439@PH0PR05MB8448.namprd05.prod.outlook.com/

The noticable performance drops vary differently depending on the
affected CPU.

If you do not need the mitigations in your particular case, disable
those. Does performace measured improves again?

The call depth tracking mitigations mentioned in the above thread did
then land in v6.2-rc1.

Regards,
Salvatore