linux-kernel - Re: Linux 6.5 speed regression, boot VERY slow with anything systemd related

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Message-ID: <ZO7lP1JKa7ptcFUP@torres.zugschlus.de>
Date:   Wed, 30 Aug 2023 08:44:15 +0200
From:   Marc Haber <mh+linux-kernel@...schlus.de>
To:     Bagas Sanjaya <bagasdotme@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        Linux Regressions <regressions@...ts.linux.dev>,
        Linux KVM <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Tony Lindgren <tony@...mide.com>
Subject: Re: Linux 6.5 speed regression, boot VERY slow with anything systemd
 related

Hi,

while debugging in the direction of qemu/kvm continues, I think that
this is an actual problem with the serial code.

On Tue, Aug 29, 2023 at 03:00:51PM +0200, Marc Haber wrote:
> my bisect came out at
> 84a9582fd203063cd4d301204971ff2cd8327f1a being the first bad commit.
> This is a rather big one, that does not easily back out of the 6.5
> release. Sadly, just transplanting drivers/tty/serial from a 6.4.12 tree
> doesn't even build. I'm adding Tony Lindgren, the author of the commit,
> to the Cc list.

Last night, I tried hard to roll back that commit and ended up with
doing

git checkout v6.5
git checkout 84a9582fd2^ -- drivers/tty/serial/
git checkout 84a9582fd2^ -- include/linux/serial_8250.h
git checkout 84a9582fd2^ -- include/linux/serial_core.h

which resulted in a 6.5 kernel that actually works without obvious
regression on the VM in question.

Thanks to Hilko Bengen and Bastian Blank who helped with the git
gymnastics and with understanding the patch in question. I wouldn't have
been able to roll that back without their help.

Greetings
Marc

-- 
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