Re: [Qemu-devel] [PATCH] ppc/pnv: fix cores per chip for multiple cpus

[Nikunj A Dadhania]

David Gibson <address@hidden> writes:

> On Mon, Sep 11, 2017 at 10:40:10AM +0530, Nikunj A Dadhania wrote:
>> David Gibson <address@hidden> writes:
>> 
>> > On Wed, Sep 06, 2017 at 01:57:48PM +0530, Nikunj A Dadhania wrote:
>> >> When the user does not provide the cpu topology, e.g. "-smp 4", machine 
>> >> fails to
>> >> initialize 4 cpus. Compute the chip per cores depending on the number of 
>> >> chips
>> >> and smt threads.
>> >> 
>> >> Signed-off-by: Nikunj A Dadhania <address@hidden>
>> >
>> > I don't understand why simply treating smp_cores as cores per chip is 
>> > wrong.
>> 
>> We do not have SMT support and when "-smp 4" is passed, smp_cores is
>> always set to 1. So only once core with one thread finally show up in
>> the guest. Moreover, I see spapr too doing similar thing in
>> spapr_init_cpus() with boot_cores_nr.
>
> I'm ok with adding an error if smp_threads > 1, since that won't
> work.  Breaking the identity that smp_cores is the number of cores per
> socket (which should correspond to one chip) is not ok, though.
>
> I think you're misinterpreting the boot_cores_nr stuff - that's just
> about translating the number of initially online vcpus into a number
> of initially online cores.

I thought, I am doing the same here for PowerNV, number of online cores
is equal to initial online vcpus / threads per core

   int boot_cores_nr = smp_cpus / smp_threads;

Only difference that I see in PowerNV is that we have multiple chips
(max 2, at the moment)

        cores_per_chip = smp_cpus / (smp_threads * pnv->num_chips);

And in case user has provided sane smp_cores, we use it.

Regards,
Nikunj