From: David Gibson <david@gibson.dropbear.id.au>
To: Laurent Vivier <lvivier@redhat.com>
Cc: "Lukáš Doktor" <ldoktor@redhat.com>,
"Juan Quintela" <quintela@redhat.com>,
qemu-devel@nongnu.org, "Greg Kurz" <groug@kaod.org>,
"Dr . David Alan Gilbert" <dgilbert@redhat.com>,
qemu-ppc@nongnu.org, clg@kaod.org
Subject: Re: [PATCH] spapr: Fix VSMT mode when it is not supported by the kernel
Date: Wed, 20 Nov 2019 22:41:28 +1100 [thread overview]
Message-ID: <20191120114128.GN5582@umbus.fritz.box> (raw)
In-Reply-To: <0c1f57ac-0823-4268-429b-d1aee8f7f8d5@redhat.com>
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On Wed, Nov 20, 2019 at 12:28:19PM +0100, Laurent Vivier wrote:
> On 20/11/2019 10:00, Laurent Vivier wrote:
> > On 20/11/2019 05:36, David Gibson wrote:
> >> On Tue, Nov 19, 2019 at 04:45:26PM +0100, Greg Kurz wrote:
> >>> On Tue, 19 Nov 2019 15:06:51 +0100
> >>> Laurent Vivier <lvivier@redhat.com> wrote:
> >>>
> >>>> On 19/11/2019 02:00, David Gibson wrote:
> >>>>> On Fri, Nov 08, 2019 at 05:47:59PM +0100, Greg Kurz wrote:
> >>>>>> On Fri, 8 Nov 2019 16:40:35 +0100
> >>>>>> Laurent Vivier <lvivier@redhat.com> wrote:
> >>>>>>
> >>>>>>> Commit 29cb4187497d sets by default the VSMT to smp_threads,
> >>>>>>> but older kernels (< 4.13) don't support that.
> >>>>>>>
> >>>>>>> We can reasonably restore previous behavior with this kernel
> >>>>>>> to allow to run QEMU as before.
> >>>>>>>
> >>>>>>> If VSMT is not supported, VSMT will be set to MAX(8, smp_threads)
> >>>>>>> as it is done for previous machine types (< pseries-4.2)
> >>>>>>>
> >>>>>>
> >>>>>> It is usually _bad_ to base the machine behavior on host capabilities.
> >>>>>> What happens if we migrate between an older kernel and a recent one ?
> >>>>>
> >>>>> Right. We're really trying to remove instaces of such behaviour. I'd
> >>>>> prefer to completely revert Greg's original patch than to re-introduce
> >>>>> host configuration dependency into the guest configuration..
> >>>>>
> >>>>>> I understand this is to fix tests/migration-test on older kernels.
> >>>>>> Couldn't this be achieved with migration-test doing some introspection
> >>>>>> and maybe pass vsmt=8 on the QEMU command line ?
> >>>>>
> >>>>> ..adjusting the test case like this might be a better idea, though.
> >>>>>
> >>>>> What's the test setup where we're using the old kernel? I really only
> >>>>> applied the original patch on the guess that we didn't really care
> >>>>> about kernels that old. The fact you've hit this in practice makes me
> >>>>> doubt that assumption.
> >>>>>
> >>>>
> >>>> The way to fix the tests is to add "-smp threads=8" on the command line
> >>>> (for all tests, so basically in qtest_init_without_qmp_handshake(), and
> >>>> it will impact all the machine types), and we have to check if it is
> >>>
> >>> Ohhh... it isn't possible to initialize Qtest with machine specific
> >>> properties ? That's a bit unfortunate :-\
> >>
> >> Uhh... I don't see why we can't. Couldn't we just put either -machine
> >> vsmt=8 or -smp 8 into the cmd_src / cmd_dst printfs() in the
> >> strcmp(arch, "ppc64") case?
> >
> > Yes, but we need to do that to all other tests that fail. test-migration
> > is not the only one impacted by the problem (we have also pxe-test), so
> > it's why I thought to fix the problem in a generic place.
> >
> > But it seems there are only this couple of tests that are impacted so I
> > can modify both instead. I think only tests that really start CPU have
> > the problem.
> >
> > I'm going to send a patch to fix that.
>
> And again, it's a little bit more complicated than expected: setting
> vsmt to 8 works only with kvm_hv, but breaks in case of TCG or kvm_pr.
> So the test must check what is in use...
Ugh, yeah, that's getting too ugly. I think the feasible options are
either to revert the patch, or just say that upstream qemu no longer
supports a RHEL7 host.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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next prev parent reply other threads:[~2019-11-20 11:43 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-08 15:40 [PATCH] spapr: Fix VSMT mode when it is not supported by the kernel Laurent Vivier
2019-11-08 16:47 ` Greg Kurz
2019-11-08 17:03 ` Laurent Vivier
2019-11-08 17:23 ` Greg Kurz
2019-11-19 1:00 ` David Gibson
2019-11-19 14:06 ` Laurent Vivier
2019-11-19 15:45 ` Greg Kurz
2019-11-19 16:13 ` Lukáš Doktor
2019-11-20 4:39 ` David Gibson
2019-11-20 4:36 ` David Gibson
2019-11-20 7:49 ` Greg Kurz
2019-11-20 9:00 ` Laurent Vivier
2019-11-20 11:28 ` Laurent Vivier
2019-11-20 11:41 ` David Gibson [this message]
2019-11-20 11:58 ` Laurent Vivier
2019-11-20 14:28 ` Laurent Vivier
2019-11-21 2:02 ` David Gibson
2019-11-20 12:47 ` Greg Kurz
2019-11-20 13:35 ` Laurent Vivier
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