Re: [Qemu-devel] [PATCH v5 3/4] spapr: Implement H_CONFER

[Nicholas Piggin]

Greg Kurz's on July 18, 2019 3:00 am:
> On Wed, 17 Jul 2019 15:39:51 +1000
> Nicholas Piggin <address@hidden> wrote:
> 
>> This does not do directed yielding and is not quite as strict as PAPR
>> specifies in terms of precise dispatch behaviour. This generally will
>> mean suboptimal performance, rather than guest misbehaviour. Linux
>> does not rely on exact dispatch behaviour.
>> 
>> Signed-off-by: Nicholas Piggin <address@hidden>
>> ---
> 
> LGTM.
> 
> Reviewed-by: Greg Kurz <address@hidden>
> 
> Just two minor comments, see below.
> 
>> Changes since v4:
>> - Style, added justification comments, spelling.
>> - Fixed trying to dereference spapr_cpu for a -1 target.
>> 
>>  hw/ppc/spapr_hcall.c | 68 ++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 68 insertions(+)
>> 
>> diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
>> index 8b208ab259..5e655172b2 100644
>> --- a/hw/ppc/spapr_hcall.c
>> +++ b/hw/ppc/spapr_hcall.c
>> @@ -1069,6 +1069,73 @@ static target_ulong h_cede(PowerPCCPU *cpu, 
>> SpaprMachineState *spapr,
>>      return H_SUCCESS;
>>  }
>>  
>> +static target_ulong h_confer(PowerPCCPU *cpu, SpaprMachineState *spapr,
>> +                           target_ulong opcode, target_ulong *args)
>> +{
>> +    target_long target = args[0];
>> +    uint32_t dispatch = args[1];
>> +    CPUState *cs = CPU(cpu);
>> +    SpaprCpuState *spapr_cpu;
>> +
>> +    /*
>> +     * -1 means confer to all other CPUs without dispatch counter check,
>> +     *  otherwise it's a targeted confer.
>> +     */
>> +    if (target != -1) {
>> +        PowerPCCPU *target_cpu = spapr_find_cpu(target);
>> +        CPUState *target_cs = CPU(target_cpu);
>> +        unsigned int target_dispatch;
> 
> Maybe make it uint32_t to be consistent with dispatch above, and this
> is the actual return type of ldl_be_phys() ?

Sure okay.

>> +
>> +        if (!target_cs) {
> 
> This is the only user of target_cs, maybe drop it and use target_cpu
> instead ?

That probably works, I'll try.

Thanks,
Nick