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

[David Gibson <david@gibson.dropbear.id.au>]

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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)  \

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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