Re: [Qemu-devel] [PATCH v1] spapr.c: Update qemu's maxcpus for pseries machine.

[seeteena <s1seetee@linux.vnet.ibm.com>]

Thanks David for the explanation.

I thought the changes been into upstream code for pseries to limit

maxcpus to 240 instead of 1024.



On 12/01/2017 06:07 PM, David Gibson wrote:
> On Fri, Dec 01, 2017 at 04:54:09PM +0530, Seeteena Thoufeek wrote:
>> Need to adjust the max cpus supported number from error message since
>> it was conflicting with KVM's.
>>
>> Steps to Reproduce:
>> 1.boot up with
>> "-smp 64,maxcpus=102464,cores=8,threads=1,sockets=8"
>>
>> qemu-kvm: Number of SMP CPUs requested (102464) exceeds max CPUs
>> supported by machine 'pseries-rhel7.4.0alt' (1024)
>>
>> 2. On KVM machine it shows
>>
>> boot up with
>> "-m 6G,maxmem=300G,slots=256 -smp 64,maxcpus=1024,cores=8,threads=1
>> ,sockets=128"
>>
>> Number of hotpluggable cpus requested (1024) exceeds the maximum cpus
>>   supported by KVM (240)
>>
>> It seemed that 1024 was useless since KVM only support 240 so far.
>> Hence,we need to adjust it to an reasonable value 240.
>>
>> Signed-off-by: Seeteena Thoufeek <s1seetee@linux.vnet.ibm.com>
> This has been written without adequate thought and investigation.
>
> First, in upstream code there's nothing wrong with having different
> limits in qemu and kernel - the can both vary depending on various
> factors.  Secondly, the 240 limit doesn't come from the kernel
> upstream - only in RHEL.
>
> Third, it doesn't even come from the kernel in RHEL - the downstream
> qemu lies about the kernel limit.
>
> I'm in the process of fixing this correctly, I expect to have
> something on Monday.
>
>> ---
>>   hw/ppc/spapr.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
>> index 9efddea..c753254 100644
>> --- a/hw/ppc/spapr.c
>> +++ b/hw/ppc/spapr.c
>> @@ -3691,6 +3691,7 @@ static const TypeInfo spapr_machine_info = {
>>           if (latest) {                                                \
>>               mc->alias = "pseries";                                   \
>>               mc->is_default = 1;                                      \
>> +            mc->max_cpus = 240;                                      \
>>           }                                                            \
>>       }                                                                \
>>       static void spapr_machine_##suffix##_instance_init(Object *obj)  \