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SubjectRe: Performance Regression in Linux Kernel 5.19
On Fri, Sep 09, 2022 at 11:46:08AM +0000, Manikandan Jagatheesan wrote:
> As part of VMware's performance regression testing for Linux
> Kernel upstream releases, we have evaluated the performance
> of Linux kernel 5.19 against the 5.18 release and we have
> noticed performance regressions in Linux VMs on ESXi as shown
> below.
> - Compute(up to -70%)
> - Networking(up to -30%)
> - Storage(up to -13%)
>
> After performing the bisect between kernel 5.18 and 5.19, we
> identified the root cause to be the enablement of IBRS mitigation
> for spectre_v2 vulnerability by commit 6ad0ad2bf8a6 ("x86/bugs:
> Report Intel retbleed vulnerability").
>
> To confirm this, we have disabled the above security mitigation
> through kernel boot parameter(spectre_v2=off) in 5.19 and re-ran
> our tests & confirmed that the performance was on-par with
> 5.18 release.

Well, duh.. :-)

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