>>You mean:
>>-cpu qemu64,+pcid
yes.
(don't known the perf difference between qemu64 (without pcid), and intel cpu
model (without pcid too) ? )
----- Mail original -----
De: "Stefan Priebe, Profihost AG" <s.pri...@profihost.ag>
À: "aderumier" <aderum...@odiso.com>
Cc: "pve-devel" <pve-devel@pve.proxmox.com>
Envoyé: Mardi 9 Janvier 2018 12:57:30
Objet: Re: [pve-devel] cpuflag: pcid needed in guest for good performance after
meltdown
Am 09.01.2018 um 12:55 schrieb Alexandre DERUMIER:
>>> Yes - see an example which does a lot of syscalls:
>
> and for qemu64 ? (is it possible to sent +pcid too ?)
You mean:
-cpu qemu64,+pcid
?
Stefan
> ----- Mail original -----
> De: "Stefan Priebe, Profihost AG" <s.pri...@profihost.ag>
> À: "aderumier" <aderum...@odiso.com>
> Cc: "pve-devel" <pve-devel@pve.proxmox.com>
> Envoyé: Mardi 9 Janvier 2018 12:20:04
> Objet: Re: [pve-devel] cpuflag: pcid needed in guest for good performance
> after meltdown
>
> Am 09.01.2018 um 10:43 schrieb Alexandre DERUMIER:
>>>> That's bad as pcid is very important to performance for meltdown fixes
>>>> in the linux kernel.
>>
>> I wonder the difference of performance for
>>
>> - qemu64|kvm64 cpu model
>> - intel cpu model
>> - intel + pcid cpu model ?
>>
>> (currently I'm running mainly qemu64 because I don't need advanced cpu flag)
>>
>> Do you have already done some benchmarks ?
>
>
> Yes - see an example which does a lot of syscalls:
>
> no tasks running other than du:
>
> no pcid:
> # time for i in $(seq 1 1 50); do du -sx /; done
> ...
> real 0m26.614s
> user 0m17.548s
> sys 0m9.056s
>
>
> kvm started with +pcid:
> # time for i in $(seq 1 1 50); do du -sx /; done
> ...
> real 0m14.734s
> user 0m7.755s
> sys 0m6.973s
>
> Greets,
> Stefan
>
>>
>> ----- Mail original -----
>> De: "Stefan Priebe, Profihost AG" <s.pri...@profihost.ag>
>> À: "aderumier" <aderum...@odiso.com>
>> Cc: "pve-devel" <pve-devel@pve.proxmox.com>
>> Envoyé: Mardi 9 Janvier 2018 10:20:39
>> Objet: Re: [pve-devel] cpuflag: pcid needed in guest for good performance
>> after meltdown
>>
>> 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
>>>> _______________________________________________
>>>> pve-devel mailing list
>>>> pve-devel@pve.proxmox.com
>>>> https://pve.proxmox.com/cgi-bin/mailman/listinfo/pve-devel
>>>>
>>>> _______________________________________________
>>>> pve-devel mailing list
>>>> pve-devel@pve.proxmox.com
>>>> https://pve.proxmox.com/cgi-bin/mailman/listinfo/pve-devel
>>>>
>>>
>>
>
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