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

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Message-ID: <ZPEPFJ8QvubbD3H9@google.com>
Date:   Thu, 31 Aug 2023 15:07:16 -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:
> Hi,
> 
> On Tue, Aug 29, 2023 at 10:14:23AM -0700, Sean Christopherson wrote:
> > On Tue, Aug 29, 2023, Marc Haber wrote:
> > > Both come from virt-manager, so if the XML helps more, I'll happy to
> > > post that as well.
> > 
> > Those command lines are quite different, e.g. the Intel one has two
> > serial ports versus one for the AMD VM.
> 
> Indeed? I virt-manager, I don't see a second serial port. In either case,
> only the one showing up in the VM as ttyS0 is being used. But thanks for
> making me look, I discovered that the machine on the Intel host still
> used emulated SCSI instead of VirtIO für the main disk. I changed that.
> 
> >Unless Tony jumps in with an
> > idea, I would try massaging either the good or bad VM's QEMU
> > invocation, e.g. see if you can get the AMD VM to "pass" by pulling in
> > stuff from the Intel VM, or get the Intel VM to fail by making its
> > command line look more like the AMD VM.
> 
> In Virt-Manager, both machines don't look THAT different tbh. I verified
> the XML and the differences are not big at all.
> 
> Do you want me to try different vCPU types? Currently the VM is set to
> "Opteron_G3", would you recommend a different vCPU for the host having a
> "AMD GX-412TC SOC" host CPU?

I would be surprised if using a different vCPU type fixed anything, but it's not
impossible that it could help.  In general, unless someone from the serial driver
side spots an issue, fixing whatever the bug is will likely require a reproducer,
which in turn likely means narrowing down what exactly is unique about your AMD
setup.  In other words, if you have cycles to spare, anything you can do to help
isolate the problem would be appreciated.