RE: Performance Regression in Linux Kernel 5.19

[David Laight]

From: Manikandan Jagatheesan
> Sent: 09 September 2022 12:46
> 
> 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").

As a matter of interest how much faster does it go if you
boot with all mitigations disabled and compile without
retpolines and without page table separation?

There are plenty of semi-embedded systems (even running on x86)
where there are a limited set of binaries, it is difficult to
add new binaries, and everything basically runs as root.

	David

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