[pve-devel] [PATCH pve-manager] qemu: bump max cores to 256 by socket

[pve-devel] [PATCH pve-manager] qemu: bump max cores to 256 by socket

[Alexandre Derumier]

New epyc cpu already support 168 threads

qemu 8.1 support 1024 cores with q35
---
 www/manager6/qemu/ProcessorEdit.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/www/manager6/qemu/ProcessorEdit.js b/www/manager6/qemu/ProcessorEdit.js
index b845ff66..b3538727 100644
--- a/www/manager6/qemu/ProcessorEdit.js
+++ b/www/manager6/qemu/ProcessorEdit.js
@@ -125,7 +125,7 @@ Ext.define('PVE.qemu.ProcessorInputPanel', {
 	    xtype: 'proxmoxintegerfield',
 	    name: 'cores',
 	    minValue: 1,
-	    maxValue: 128,
+	    maxValue: 256,
 	    value: '1',
 	    fieldLabel: gettext('Cores'),
 	    allowBlank: false,
-- 
2.39.2

Re: [pve-devel] [PATCH pve-manager] qemu: bump max cores to 256 by socket

[Dominik Csapak]

On 1/12/24 21:08, Alexandre Derumier wrote:
> New epyc cpu already support 168 threads
> 
> qemu 8.1 support 1024 cores with q35
> ---
>   www/manager6/qemu/ProcessorEdit.js | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/www/manager6/qemu/ProcessorEdit.js b/www/manager6/qemu/ProcessorEdit.js
> index b845ff66..b3538727 100644
> --- a/www/manager6/qemu/ProcessorEdit.js
> +++ b/www/manager6/qemu/ProcessorEdit.js
> @@ -125,7 +125,7 @@ Ext.define('PVE.qemu.ProcessorInputPanel', {
>   	    xtype: 'proxmoxintegerfield',
>   	    name: 'cores',
>   	    minValue: 1,
> -	    maxValue: 128,
> +	    maxValue: 256,
>   	    value: '1',
>   	    fieldLabel: gettext('Cores'),
>   	    allowBlank: false,


mhmm.. in the backend we don't actually have a limit, maybe it's time to remove the limit in the ui
altogether? it does not help anyway:

for numbers that are not too big (too many for qemu, too many for the host)
it's not the right limit (qemu) or we don't know at that point in the gui (host cores)

but in case next year there is e.g. a 512 core machine, the limit is too low again...


so i'd be either for
* removing the limit at all
* limit to the qemu limits (but maybe also in the backend?)
* use the number of cores of the current host as limit in the gui (should be possible, but an 
additional api call)

what do you think?

Re: [pve-devel] [PATCH pve-manager] qemu: bump max cores to 256 by socket

[DERUMIER, Alexandre]

>>mhmm.. in the backend we don't actually have a limit, maybe it's time
>>to remove the limit in the ui
>>altogether? it does not help anyway:

>>for numbers that are not too big (too many for qemu, too many for the
>>host)
>>it's not the right limit (qemu) or we don't know at that point in the
>>gui (host cores)

>>but in case next year there is e.g. a 512 core machine, the limit is
>>too low again...


>>so i'd be either for
>>* removing the limit at all
>>* limit to the qemu limits (but maybe also in the backend?)
>>* use the number of cores of the current host as limit in the gui
>>(should be possible, but an 
>>additional api call)
>>
>>what do you think?


Yes, indeed the backend don't have any limit.

We could indeed remove the limit in the gui.

I think we shouldn't limit based on the current host, as anyway, we can
create && migrate the vm on antoher host just after the create.


Maybe an improvement in qemu-server, could be to add additional check
at vm start, (maybe a simple warn), depending of qemu version or
setup. 
For example, 1024 cores only works with q35 && qemu 8.1,
it could be interesting to give an clean hint  mesage to user instead
a qemu process error.

Re: [pve-devel] [PATCH pve-manager] qemu: bump max cores to 256 by socket

[Fiona Ebner]

Am 15.01.24 um 13:43 schrieb DERUMIER, Alexandre:
> 
> 
> Maybe an improvement in qemu-server, could be to add additional check
> at vm start, (maybe a simple warn), depending of qemu version or
> setup. 
> For example, 1024 cores only works with q35 && qemu 8.1,
> it could be interesting to give an clean hint  mesage to user instead
> a qemu process error.
> 

Is the QEMU error message understandable? If yes, I don't see much value
in adding such a heuristic and warning ourselves. If no, we can either
improve the QEMU error message or do as you suggested.

Re: [pve-devel] [PATCH pve-manager] qemu: bump max cores to 256 by socket

[DERUMIER, Alexandre]

>>Is the QEMU error message understandable? If yes, I don't see much
>>value

Well, indeed, the message is pretty clear.
maybe just add documentation about limit for q35 && i440fx ?

(I have a customer with a new epyc v4, asking me about this, and I had
no idea that they was a different limit between q35 && i440fx)



with i440fx (and 512 cores)

# qm start 105
kvm: Invalid SMP CPUs 512. The max CPUs supported by machine 'pc-
i440fx-8.1' is 255


with q35 (and 4096 cores)

# qm start 105
kvm: Invalid SMP CPUs 4096. The max CPUs supported by machine 'pc-q35-
8.1' is 1024


-------- Message initial --------
De: Fiona Ebner <f.ebner@proxmox.com>
À: Proxmox VE development discussion <pve-devel@lists.proxmox.com>,
"DERUMIER, Alexandre" <alexandre.derumier@groupe-cyllene.com>,
d.csapak@proxmox.com <d.csapak@proxmox.com>, aderumier@odiso.com
<aderumier@odiso.com>
Objet: Re: [pve-devel] [PATCH pve-manager] qemu: bump max cores to 256
by socket
Date: 15/01/2024 14:08:39

Am 15.01.24 um 13:43 schrieb DERUMIER, Alexandre:
> 
> 
> Maybe an improvement in qemu-server, could be to add additional check
> at vm start, (maybe a simple warn), depending of qemu version or
> setup. 
> For example, 1024 cores only works with q35 && qemu 8.1,
> it could be interesting to give an clean hint  mesage to user instead
> a qemu process error.
> 

Is the QEMU error message understandable? If yes, I don't see much
value
in adding such a heuristic and warning ourselves. If no, we can either
improve the QEMU error message or do as you suggested.

Re: [pve-devel] [PATCH pve-manager] qemu: bump max cores to 256 by socket

[Fiona Ebner]

Am 16.01.24 um 15:08 schrieb DERUMIER, Alexandre:
> 
>>> Is the QEMU error message understandable? If yes, I don't see much
>>> value
> 
> Well, indeed, the message is pretty clear.
> maybe just add documentation about limit for q35 && i440fx ?
> 
> (I have a customer with a new epyc v4, asking me about this, and I had
> no idea that they was a different limit between q35 && i440fx)
> 

Sure, we can mention that the limit depends on the machine version in
the CPU section and/or machine version section. Note it's not only type,
but version, e.g. q35-8.0 has 288 as a limit:
https://github.com/qemu/qemu/blob/master/hw/i386/pc_q35.c#L419

[pve-devel] applied: [PATCH pve-manager] qemu: bump max cores to 256 by socket

[Thomas Lamprecht]

Am 12/01/2024 um 21:08 schrieb Alexandre Derumier:
> New epyc cpu already support 168 threads
> 
> qemu 8.1 support 1024 cores with q35
> ---
>  www/manager6/qemu/ProcessorEdit.js | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
>

applied, as even though removing the maximum here (or upping it to
something really high like 8192), can be argued for this patch
is already here and better than nothing, thanks!

ps. please remember to sign-off your patches, maybe adding an alias
like `git config --global alias.ci 'commit -s` could help.