netdev - Re: Fwd: High cpu usage caused by kernel process when upgraded to linux 5.19.17 or later

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Date: Thu, 29 Jun 2023 16:18:57 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Vivek Anand <vivekanand754@...il.com>, Peter Zijlstra
 <peterz@...radead.org>
Cc: Bagas Sanjaya <bagasdotme@...il.com>, "Steven Rostedt (Google)"
 <rostedt@...dmis.org>, Pablo Neira Ayuso <pablo@...filter.org>, Jozsef
 Kadlecsik <kadlec@...filter.org>, Florian Westphal <fw@...len.de>, "David
 S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Lingutla Chandrasekhar <clingutla@...eaurora.org>, Frederic Weisbecker
 <frederic@...nel.org>, "J. Avila" <elavila@...gle.com>, "Rafael J.
 Wysocki" <rafael@...nel.org>, Thomas Renninger <trenn@...e.com>, Shuah
 Khan <shuah@...nel.org>, Borislav Petkov <bp@...en8.de>, Josh Poimboeuf
 <jpoimboe@...nel.org>, Linux Kernel Mailing List
 <linux-kernel@...r.kernel.org>, Linux Regressions
 <regressions@...ts.linux.dev>, Linux Netfilter Development
 <netfilter-devel@...r.kernel.org>, Netfilter Core Developers
 <coreteam@...filter.org>, Linux Networking <netdev@...r.kernel.org>, Linux
 Power Management <linux-pm@...r.kernel.org>, x86@...nel.org
Subject: Re: Fwd: High cpu usage caused by kernel process when upgraded to
 linux 5.19.17 or later

On Thu, Jun 29 2023 at 12:05, Vivek Anand wrote:
> I've tried booting with "spectre_v2=retpoline retbleed=off".
> This change didn't work. Still CPU is 100%

This does not make sense.

retbleed=off has the same effect as CONFIG_X86_IBRS_ENTRY=n.

The only difference is that with CONFIG_X86_IBRS_ENTRY=y and
retbleed=off there is one extra jump in the low level entry code
(syscall, interrupts, exceptions) and one extra jump on the exit side.

But those extra jumps are completely irrelevant for the kworker threads.

Can you please provide dmesg and the content of the files in

 /sys/devices/system/cpu/vulnerabilities/

on a kernel booted with "spectre_v2=retpoline retbleed=off" ?

Thanks,

        tglx