ok thanks !
----- 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 14:10:27
Objet: Re: [pve-devel] cpuflag: pcid needed in guest for good performance after
meltdown
Am 09.01.2018 um 13:02 schrieb Alexandre DERUMIER:
>>> You mean:
>>> -cpu qemu64,+pcid
>
> yes.
>
> (don't known the perf difference between qemu64 (without pcid), and intel cpu
> model (without pcid too) ? )
The results are nearly the same.
Same VM as before now model qemu64,+pcid:
real 0m13.870s
user 0m7.128s
sys 0m6.697s
qemu64:
real 0m25.214s
user 0m16.923s
sys 0m8.956s
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 12:57:30
> 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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