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Date:   Wed, 6 Sep 2023 18:26:16 +0300
From:   Tony Lindgren <tony@atomide.com>
To:     Marc Haber <mh+linux-kernel@zugschlus.de>
Cc:     Sean Christopherson <seanjc@google.com>,
        Bagas Sanjaya <bagasdotme@gmail.com>,
        linux-kernel@vger.kernel.org,
        Linux Regressions <regressions@lists.linux.dev>,
        Linux KVM <kvm@vger.kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: Linux 6.5 speed regression, boot VERY slow with anything systemd
 related
Message-ID: <20230906152616.GE11676@atomide.com>
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* Marc Haber <mh+linux-kernel@zugschlus.de> [230906 14:41]:
> With my tools I have found out that it really seems to be related to the
> CPU of the host. I have changed my VM definition to "copy host CPU
> configuration to VM" in libvirt and have moved this very VM (image and
> settings) to hosts with a "Ryzen 5 Pro 4650G" and to an "Intel Xeon
> E3-1246" where they work flawlessly, while on both APUs I have available
> ("AMD G-T40E" and "AMD GX-412TC SOC") the regression in 6.5 shows. And
> if I boot other VMs on the APUs with 6.5 the issue comes up. It is a
> clear regression since going back to 4.6's serial code solves the issue
> on the APUs.

Not sure why the CPU matters here..

One thing to check is if you have these in your .config:

CONFIG_SERIAL_CORE=y
CONFIG_SERIAL_CORE_CONSOLE=y

Or do you maybe have CONFIG_SERIAL_CORE=m as loadable module?

If you have CONFIG_SERIAL_CORE=m, maybe you need to modprobe serial_base
if you have some minimal rootfs that does not automatically do it for you.

Regards,

Tony