From: Greg Kurz <email@example.com>
To: David Gibson <firstname.lastname@example.org>
Cc: email@example.com, "Thomas Huth" <firstname.lastname@example.org>,
"Cédric Le Goater" <email@example.com>
Subject: Re: [Qemu-devel] [PATCH for-3.1] tests/cpu-plug-test: check CPU hotplug on ppc64 with KVM
Date: Mon, 30 Jul 2018 10:41:45 +0200 [thread overview]
Message-ID: <firstname.lastname@example.org> (raw)
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On Mon, 30 Jul 2018 15:57:15 +1000
David Gibson <email@example.com> wrote:
> On Fri, Jul 27, 2018 at 09:54:52AM +0200, Greg Kurz wrote:
> > On Fri, 27 Jul 2018 15:27:24 +1000
> > David Gibson <firstname.lastname@example.org> wrote:
> > > On Wed, Jul 25, 2018 at 04:45:26PM +0200, Greg Kurz wrote:
> > > > Commit b585395b655 fixed a regression introduced by some recent changes
> > > > in the XICS code, that was causing QEMU to crash instantly during CPU
> > > > hotplug with KVM. This is typically the kind of bug we'd like our
> > > > test suite to detect before it gets merged. Unfortunately, the current
> > > > tests run with '-machine accel=qtest' and don't exercise KVM specific
> > > > paths in QEMU.
> > > >
> > > > This patch hence changes add_pseries_test_case() to launch QEMU with
> > > > '-machine accel=kvm' if KVM is available.
> > > >
> > > > A notable consequence is that the guest will execute SLOF, but for some
> > > > reasons SLOF sometimes hits a program exception. This causes the guest
> > > > to loop forever and the test to be stuck. Since we don't need the guest
> > > > to be truely running, let's pass -S to QEMU to avoid that.
> > > >
> > > > Also disable machine capabilities that could be unavailable in KVM, eg,
> > > > when using PR KVM.
> > > >
> > > > Signed-off-by: Greg Kurz <email@example.com>
> > >
> > > I'm pretty sure trying to change the accelerator on a qtest test just
> > > doesn't make sense. We'd need a different approach for testing cpu
> > > hotplug against kvm & tcg backends.
> > >
> > The test starts QEMU, triggers the CPU hotplug code with a QMP command
> > and checks the command didn't fail (or QEMU didn't crash, as it would
> > have before commit b585395b655a)... I really don't understand what
> > is wrong with that... Please elaborate.
> Well, ok, let me turn that around. A test that doesn't rely on
> controlling the guest side behaviour at all probably shouldn't be a
> qtest based test, since that's what qtest is all about.
The CPU hotplug test doesn't seem to do anything on the guest side: it
just checks that 'device_add' returns a response that isn't an error.
I'm not aware that the guest is expected to have a specific behavior
during 'device_add', apart from not crashing or hanging. That was the
initial idea behind passing '-S' to ensure the guest doesn't run.
Your remark seems to be more general though... are you meaning that
doing something like qtest_start("-machine accel=kvm:tcg") is just
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next prev parent reply other threads:[~2018-07-30 8:42 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-25 14:45 [Qemu-devel] [PATCH for-3.1] tests/cpu-plug-test: check CPU hotplug on ppc64 with KVM Greg Kurz
2018-07-27 5:27 ` David Gibson
2018-07-27 7:54 ` Greg Kurz
2018-07-27 8:18 ` Thomas Huth
2018-07-27 9:00 ` Greg Kurz
2018-07-27 11:25 ` Thomas Huth
2018-07-27 12:03 ` Greg Kurz
2018-07-30 5:57 ` David Gibson
2018-07-30 8:41 ` Greg Kurz [this message]
2018-07-30 9:59 ` Greg Kurz
2018-07-31 3:27 ` David Gibson
2018-08-01 13:35 ` Greg Kurz
2018-07-31 3:25 ` David Gibson
2018-08-01 13:24 ` Greg Kurz
2018-08-02 4:08 ` David Gibson
2018-08-02 9:36 ` Igor Mammedov
2018-08-02 10:52 ` Greg Kurz
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