CPU performance - disable bug mitigations

Goran sendmailtogoran at gmail.com
Tue Nov 20 16:05:08 UTC 2018

Hi all,

I have some servers with AMD Opteron 6276 CPUs and doing some number
crunching on these.

I installed Ubuntu 16.04 and was pretty much satisfied (never did an
update - running local only). Some days ago I installed 18.04 and got
a performance penalty of 33%.

My guess is, that it has something to do with Spectre. So I did a

# grep . /sys/devices/system/cpu/vulnerabilities/*
/sys/devices/system/cpu/vulnerabilities/meltdown:Not affected
Speculative Store Bypass disabled via prctl and seccomp
/sys/devices/system/cpu/vulnerabilities/spectre_v1:Mitigation: __user
pointer sanitization
/sys/devices/system/cpu/vulnerabilities/spectre_v2:Mitigation: Full
AMD retpoline, IBPB

How can I disable these mitigations without restart (without boot
command line)? I just found some examples for Red Hat which are not
working for Ubuntu.

Further I read these pages:

I would like to disable all mitigations related to any of these hardware-bugs.

After all I got the harshest penalty when I switched back to 16.04.5
(fresh new install) and could not get my performance back. My old
16.04 is lost so no way back.

How to get back my performance?


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