Am 09.01.2018 um 09:18 schrieb Alexandre DERUMIER:
> they are a discussion on qemu mailing currently about pcid
>
>
> From paolo bonzini:
>
> "
> Note that PCID is still not supported for guests without EPT, so
> this would break ept=0 with recent "-cpu" models. I'm not sure of
> a way to fix it; probably it just has to be documented."
That's bad as pcid is very important to performance for meltdown fixes
in the linux kernel.
Stefan
>
> ----- Mail original -----
> De: "Stefan Priebe, Profihost AG" <s.pri...@profihost.ag>
> À: "pve-devel" <pve-devel@pve.proxmox.com>, "aderumier" <aderum...@odiso.com>
> Envoyé: Mardi 9 Janvier 2018 08:35:00
> Objet: Re: [pve-devel] cpuflag: pcid needed in guest for good performance
> after meltdown
>
> Am 08.01.2018 um 23:23 schrieb Alexandre DERUMIER:
>> I think it's not exposed in current cpu model
>>
>> it can be enabled with "+pcid"
>>
>>
>> I don't known what it's the best way to add it in proxmox.
>> We could do it with qemu version upgrade, but qemu 2.10 are not ready.
>
> Yes but that was always bad at least to me. We're limiting ourselfes if
> we can only add new qemu features with a new qemu version.
>
> What about a version or feature field in the guest config which we only
> update on a fresh vm start.
>
> Something like this:
> 123.conf:
> ...
> pve_qemu_version: 2.11-10
> ...
>
> This field is ONLY and ALWAYS updated in a fresh start not on migration.
> This can be easily detected.
>
> Than we can do stuff like
> if (version_cmp($conf->{pve_qemu_version}, "2.11-11")) {
> # enable pcid flag
> }
>
> Greets
> Stefan
>
>> Maybe add new cpumodel with +pcid enabled ?
>> or add code to manage custom cpuflags and add a checkbox in cpu options ?
>>
>>
>>
>> ----- Mail original -----
>> De: "Stefan Priebe, Profihost AG" <s.pri...@profihost.ag>
>> À: "pve-devel" <pve-devel@pve.proxmox.com>
>> Envoyé: Lundi 8 Janvier 2018 21:34:57
>> Objet: [pve-devel] cpuflag: pcid needed in guest for good performance after
>> meltdown
>>
>> Hello,
>>
>> for meltdown mitigation and performance it's important to have the pcid
>> flag passed down to the guest (f.e.
>> https://groups.google.com/forum/m/#!topic/mechanical-sympathy/L9mHTbeQLNU).
>>
>> My host shows the flag:
>> # grep ' pcid ' /proc/cpuinfo | wc -l
>> 56
>>
>> But the guest does not:
>> # grep pcid /proc/cpuinfo
>> #
>>
>> Guest was started with:
>> -cpu IvyBridge,+kvm_pv_unhalt,+kvm_pv_eoi,enforce,vendor=GenuineIntel
>>
>> Is this something missing in host kernel or in PVE?
>>
>> Greets,
>> Stefan
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>>
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>>
>
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