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Re: [Qemu-devel] [PATCH v13 3/5] i386: Enable TOPOEXT feature on AMD EPY
From: |
Eduardo Habkost |
Subject: |
Re: [Qemu-devel] [PATCH v13 3/5] i386: Enable TOPOEXT feature on AMD EPYC CPU |
Date: |
Tue, 12 Jun 2018 16:05:54 -0300 |
User-agent: |
Mutt/1.9.2 (2017-12-15) |
On Tue, Jun 12, 2018 at 06:38:08PM +0000, Moger, Babu wrote:
[...]
> > I'm starting to think that enabling TOPOEXT automatically is
> > adding too much complexity and compatibility problems, and it's
> > better to leave this task to management software.
> >
> > The main problem here is:
> >
> > This works today with QEMU 2.12 + Linux <= 4.15:
> > $ $QEMU -machine pc -cpu EPYC,enforce -smp
> > 8,sockets=2,cores=2,threads=2"
> > and must keep working with QEMU 3.0 and Linux <= 4.15.
> >
> > In addition to that, the results for:
> > $ $QEMU -machine pc-q35-3.0 -cpu EPYC,enforce [...]
> > must be deterministic and expose exactly the same CPUID data even
> > if host hardware or software changes, as long as the QEMU
> > command-line is the same.
> >
> > Do you see a way to fulfill those two constraints while making
> > "-machine pc-q35-3.0 -cpu EPYC" enable TOPOEXT automatically?
> >
>
> Now(setting feature before x86_cpu_expand_features), enabling
> TOPOEXT appears to work fine.
What about the above constraints? Are you really fulfilling
them?
This one is tricky:
] This works today with QEMU 2.12 + Linux <= 4.15:
] $ $QEMU -machine pc -cpu EPYC,enforce -smp 8,sockets=2,cores=2,threads=2"
] and must keep working with QEMU 3.0 and Linux <= 4.15.
If we enable TOPOEXT unconditionally, the command-line won't work
with Linux <= 4.15.
If we enable TOPOEXT only if the kernel returns TOPOEXT on
GET_SUPPORTED_CPUID, we break the second constraint:
] The results for:
] $ $QEMU -machine pc-q35-3.0 -cpu EPYC,enforce [...]
] must be deterministic and expose exactly the same CPUID data even
] if host hardware or software changes, as long as the QEMU
] command-line is the same.
--
Eduardo
- [Qemu-devel] [PATCH v13 1/5] i386: Add support for CPUID_8000_001E for AMD, (continued)
- [Qemu-devel] [PATCH v13 1/5] i386: Add support for CPUID_8000_001E for AMD, Babu Moger, 2018/06/08
- [Qemu-devel] [PATCH v13 3/5] i386: Enable TOPOEXT feature on AMD EPYC CPU, Babu Moger, 2018/06/08
- Re: [Qemu-devel] [PATCH v13 3/5] i386: Enable TOPOEXT feature on AMD EPYC CPU, Eduardo Habkost, 2018/06/11
- Re: [Qemu-devel] [PATCH v13 3/5] i386: Enable TOPOEXT feature on AMD EPYC CPU, Moger, Babu, 2018/06/11
- Re: [Qemu-devel] [PATCH v13 3/5] i386: Enable TOPOEXT feature on AMD EPYC CPU, Eduardo Habkost, 2018/06/11
- Re: [Qemu-devel] [PATCH v13 3/5] i386: Enable TOPOEXT feature on AMD EPYC CPU, Moger, Babu, 2018/06/12
- Re: [Qemu-devel] [PATCH v13 3/5] i386: Enable TOPOEXT feature on AMD EPYC CPU, Eduardo Habkost, 2018/06/12
- Re: [Qemu-devel] [PATCH v13 3/5] i386: Enable TOPOEXT feature on AMD EPYC CPU, Moger, Babu, 2018/06/12
- Re: [Qemu-devel] [PATCH v13 3/5] i386: Enable TOPOEXT feature on AMD EPYC CPU,
Eduardo Habkost <=
- Re: [Qemu-devel] [PATCH v13 3/5] i386: Enable TOPOEXT feature on AMD EPYC CPU, Babu Moger, 2018/06/12
- Re: [Qemu-devel] [PATCH v13 3/5] i386: Enable TOPOEXT feature on AMD EPYC CPU, Moger, Babu, 2018/06/13
- Re: [Qemu-devel] [PATCH v13 3/5] i386: Enable TOPOEXT feature on AMD EPYC CPU, Eduardo Habkost, 2018/06/13
- Re: [Qemu-devel] [PATCH v13 3/5] i386: Enable TOPOEXT feature on AMD EPYC CPU, Moger, Babu, 2018/06/13
- Re: [Qemu-devel] [PATCH v13 3/5] i386: Enable TOPOEXT feature on AMD EPYC CPU, Moger, Babu, 2018/06/13
- Re: [Qemu-devel] [PATCH v13 3/5] i386: Enable TOPOEXT feature on AMD EPYC CPU, Eduardo Habkost, 2018/06/13
- Re: [Qemu-devel] [PATCH v13 3/5] i386: Enable TOPOEXT feature on AMD EPYC CPU, Moger, Babu, 2018/06/13
- Re: [Qemu-devel] [PATCH v13 3/5] i386: Enable TOPOEXT feature on AMD EPYC CPU, Eduardo Habkost, 2018/06/13
- Re: [Qemu-devel] [PATCH v13 3/5] i386: Enable TOPOEXT feature on AMD EPYC CPU, Moger, Babu, 2018/06/13
[Qemu-devel] [PATCH v13 4/5] i386: Verify and enable topoext feature if supported, Babu Moger, 2018/06/08