Re: [Qemu-ppc] [Qemu-devel] [PATCH RFC 2/4] target-ppc: with MTTCG report more threads

[Nikunj A Dadhania]

Greg Kurz <address@hidden> writes:

> On Fri, 02 Sep 2016 15:04:47 +0530
> Nikunj A Dadhania <address@hidden> wrote:
>
>> Greg Kurz <address@hidden> writes:
>> 
>> > On Fri,  2 Sep 2016 12:02:54 +0530
>> > Nikunj A Dadhania <address@hidden> wrote:
>> >  
>> >> Signed-off-by: Nikunj A Dadhania <address@hidden>
>> >> ---  
>> >
>> > Shouldn't this patch be the last one, when all other issues have been 
>> > addressed ?
>> >  
>> >>  target-ppc/kvm.c     | 2 +-
>> >>  target-ppc/kvm_ppc.h | 2 +-
>> >>  2 files changed, 2 insertions(+), 2 deletions(-)
>> >> 
>> >> diff --git a/target-ppc/kvm.c b/target-ppc/kvm.c
>> >> index dcb68b9..20eb450 100644
>> >> --- a/target-ppc/kvm.c
>> >> +++ b/target-ppc/kvm.c
>> >> @@ -2090,7 +2090,7 @@ void kvmppc_set_mpic_proxy(PowerPCCPU *cpu, int 
>> >> mpic_proxy)
>> >>  
>> >>  int kvmppc_smt_threads(void)
>> >>  {
>> >> -    return cap_ppc_smt ? cap_ppc_smt : 1;
>> >> +    return cap_ppc_smt ? cap_ppc_smt : 8;  
>> >
>> > If KVM is there but does not support SMT processor modes, it looks
>> > wrong to return anything but 1. This check needs kvm_enabled().  
>> 
>> This also gets called when emulating PPC on PPC. 
>> 
>
> Yes and the current value of 1 is the default for non HV KVM and TCG. If
> you want to change the default for MTTCG, then you need separate paths.
>
>> > Also, why 8 ? This depends on the CPU model.  
>> 
>> Not sure if I need to emulate according to the host cpu model. I had
>> selected 8, as that was the highest number of threads possible for POWER.
>> 
>
> If running in full emulation and cpu type is POWER7, this shouldn't be
> higher than 4.
>
> In the end, something like:
>
> int kvmppc_smt_threads(void)
> {
>     if (kvm_enabled()) {
>         return cap_ppc_smt ? cap_ppc_smt : 1;
>     } else {
>         return 8_or_4_or_2_or_1_depending_on_the_cpu_model;
>     }
> }

Sure, will need something like this.

Regards,
Nikunj