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Re: [PATCH] spapr: Fix VSMT mode when it is not supported by the kernel
From: |
Laurent Vivier |
Subject: |
Re: [PATCH] spapr: Fix VSMT mode when it is not supported by the kernel |
Date: |
Tue, 19 Nov 2019 15:06:51 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 |
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 <address@hidden> 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
ppc64/pseries to do that, and there it becomes a little bit complicated
for a so small piece of code.
So I think the best to do is to revert Greg's patch.
Thanks,
Laurent
- [PATCH] spapr: Fix VSMT mode when it is not supported by the kernel, Laurent Vivier, 2019/11/08
- Re: [PATCH] spapr: Fix VSMT mode when it is not supported by the kernel, Greg Kurz, 2019/11/08
- Re: [PATCH] spapr: Fix VSMT mode when it is not supported by the kernel, Laurent Vivier, 2019/11/08
- Re: [PATCH] spapr: Fix VSMT mode when it is not supported by the kernel, David Gibson, 2019/11/18
- Re: [PATCH] spapr: Fix VSMT mode when it is not supported by the kernel, David Gibson, 2019/11/19
- Re: [PATCH] spapr: Fix VSMT mode when it is not supported by the kernel, Greg Kurz, 2019/11/20
- Re: [PATCH] spapr: Fix VSMT mode when it is not supported by the kernel, Laurent Vivier, 2019/11/20
- Re: [PATCH] spapr: Fix VSMT mode when it is not supported by the kernel, Laurent Vivier, 2019/11/20
- Re: [PATCH] spapr: Fix VSMT mode when it is not supported by the kernel, David Gibson, 2019/11/20
- Re: [PATCH] spapr: Fix VSMT mode when it is not supported by the kernel, Laurent Vivier, 2019/11/20
- Re: [PATCH] spapr: Fix VSMT mode when it is not supported by the kernel, Laurent Vivier, 2019/11/20