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

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Message-ID: <ZO4GeazfcA09SfKw@google.com>
Date:   Tue, 29 Aug 2023 07:53:45 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Marc Haber <mh+linux-kernel@...schlus.de>
Cc:     Bagas Sanjaya <bagasdotme@...il.com>, linux-kernel@...r.kernel.org,
        Linux Regressions <regressions@...ts.linux.dev>,
        Linux KVM <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Tony Lindgren <tony@...mide.com>
Subject: Re: Linux 6.5 speed regression, boot VERY slow with anything systemd related

On Tue, Aug 29, 2023, Marc Haber wrote:
> [Please keep me on Cc, I am only subscribed to linux-kernel]
> 
> Hi Bagas,
> 
> thanks for your quick answer.
> 
> On Tue, Aug 29, 2023 at 03:17:15PM +0700, Bagas Sanjaya wrote:
> > In any case, bisecting kernel is highly appreciated in order to pin down
> > the culprit.
> 
> Without having read the docs (that came too late, need to read up on
> that again), 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.
> 
> But, since the commit is related to serial port, I began fiddling around
> with the serial port setting on the misbehaving VM and found out that
> running the VM without the serial console that I am using (thus removing
> "console=ttyS0,57600n8" from the kernel command line) makes the machine
> boot up just fine with the 6.5 kernel that I built yesterday. It is not
> even necessary to remove the virtual serial port.
> 
> The issue is still somehow connected to the host the machine is running
> on, since my VMs all have a serial console and the test VMs running on
> different hosts are running fine with 6.5.

What is different between the bad host(s) and the good host(s)?  E.g. kernel, QEMU,
etc.