[PATCH] pc: q35: Bump max_cpus to 1024

[PATCH] pc: q35: Bump max_cpus to 1024

[Dario Faggioli]

Keep the old limit of 288 for machine versions 7.2 and earlier.

Signed-off-by: Dario Faggioli <dfaggioli@suse.com>
---
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Eduardo Habkost <eduardo@habkost.net>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
---
This is related to:

https://lore.kernel.org/qemu-devel/c705d0d8d6ed1a520b1ff92cb2f83fef19522d30.camel@suse.com/

With this applied to QEMU, I've been able to start a VM with as high as
980 vCPUs (even if I was on an host with 384 pCPUs, so everything was
super slow!). After that, I started to see messages like this:

"SMBIOS 2.1 table length 66822 exceeds 65535"

Thanks and Regards
---
 hw/i386/pc_q35.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
index a496bd6e74..d2a567a71f 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -367,7 +367,7 @@ static void pc_q35_machine_options(MachineClass *m)
     machine_class_allow_dynamic_sysbus_dev(m, TYPE_INTEL_IOMMU_DEVICE);
     machine_class_allow_dynamic_sysbus_dev(m, TYPE_RAMFB_DEVICE);
     machine_class_allow_dynamic_sysbus_dev(m, TYPE_VMBUS_BRIDGE);
-    m->max_cpus = 288;
+    m->max_cpus = 1024;
 }
 
 static void pc_q35_7_2_machine_options(MachineClass *m)
@@ -386,6 +386,7 @@ static void pc_q35_7_1_machine_options(MachineClass *m)
     PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
     pc_q35_7_2_machine_options(m);
     m->alias = NULL;
+    m->max_cpus = 288;
     pcmc->legacy_no_rng_seed = true;
     compat_props_add(m->compat_props, hw_compat_7_1, hw_compat_7_1_len);
     compat_props_add(m->compat_props, pc_compat_7_1, pc_compat_7_1_len);

Re: [PATCH] pc: q35: Bump max_cpus to 1024

[Dario Faggioli]

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Well...

On Thu, 2022-11-17 at 16:27 +0100, Dario Faggioli wrote:
> Keep the old limit of 288 for machine versions 7.2 and earlier.
> 
...At least, this was the idea...

> --- a/hw/i386/pc_q35.c
> +++ b/hw/i386/pc_q35.c
> @@ -386,6 +386,7 @@ static void
> pc_q35_7_1_machine_options(MachineClass *m)
>      PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
>      pc_q35_7_2_machine_options(m);
>      m->alias = NULL;
> +    m->max_cpus = 288;
>
...But I managed to put this in the wrong function (xxx_7_1_yyy,
instead than xxx_7_2_yyyy)! :-/

Sorry about taht. I'll send a v2 (taking the feedback that I got to my
other email into account).

Regards
-- 
Dario Faggioli, Ph.D
http://about.me/dario.faggioli
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
-------------------------------------------------------------------
<<This happens because _I_ choose it to happen!>> (Raistlin Majere)

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Re: [PATCH] pc: q35: Bump max_cpus to 1024

[Claudio Fontana]

On 11/17/22 19:04, Dario Faggioli wrote:
> Well...
> 
> On Thu, 2022-11-17 at 16:27 +0100, Dario Faggioli wrote:
>> Keep the old limit of 288 for machine versions 7.2 and earlier.
>>
> ...At least, this was the idea...
> 
>> --- a/hw/i386/pc_q35.c
>> +++ b/hw/i386/pc_q35.c
>> @@ -386,6 +386,7 @@ static void
>> pc_q35_7_1_machine_options(MachineClass *m)
>>      PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
>>      pc_q35_7_2_machine_options(m);
>>      m->alias = NULL;
>> +    m->max_cpus = 288;
>>
> ...But I managed to put this in the wrong function (xxx_7_1_yyy,
> instead than xxx_7_2_yyyy)! :-/

I was just about to comment on it :-)

> 
> Sorry about taht. I'll send a v2 (taking the feedback that I got to my
> other email into account).
> 
> Regards

Ciao,

C