Re: [Qemu-devel] [PATCH v2] ppc: introduce CPUPPCState::cpu_dt_id

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 11/04/2013 09:00 PM, Paolo Bonzini wrote:
> Il 01/11/2013 04:21, Alexey Kardashevskiy ha scritto:
>> Normally CPUState::cpu_index is used to pick the right CPU for various
>> operations. However default consecutive numbering does not always work
>> for POWERPC.
>>
>> For example, on POWER7 (which supports 4 threads per core),
>> "-smp 8,threads=4" should create CPUs with indexes 0,1,2,3,4,5,6,7 and
>> "-smp 8,threads=1" should create CPUs with indexes 0,4,8,12,16,20,24,28.
>>
>> These indexes are reflected in /proc/device-tree/cpus/PowerPC,POWER7@XX
>> and used to call KVM VCPU's ioctls. In order to achieve this,
>> kvmppc_fixup_cpu() was introduced. Roughly speaking, it multiplies
>> cpu_index by the number of threads per core.
>>
>> This approach has disadvantages such as:
>> 1. NUMA configuration stays broken after the fixup;
>> 2. CPU-related commands from QEMU Monitor do not work properly as
>> the accept fixed CPU indexes and the user does not really know
>> what they are after fixup as the number of threads per core changes
>> between CPU versions and via QEMU command line.
>>
>> This introduces a new @cpu_dt_id field in the CPUPPCState struct which
>> is set from @cpu_index by default but can be fixed later to the value
>> which a hypervisor can accept. This also introduces two POWERPC-arch
>> specific functions:
>> 1. int ppc_get_vcpu_dt_id(CPUState *cs) - returns a device-tree ID
>> for a CPU;
>> 2. CPUState *ppc_get_vcpu_by_dt_id(int cpu_dt_id) - finds CPUState by
>> a device-tree CPU ID.
>>
>> This uses the new functions to:
>> 1. fix emulated XICS hypercall handlers as they receive fixed CPU indexes;
>> 2. fix XICS-KVM to enable in-kernel XICS on right CPU;
>> 3. compose correct device-tree.
>>
>> This removes @cpu_index fixup as @cpu_dt_id is used instead so QEMU monitor
>> can accept command-line CPU indexes again.
>>
>> Cc: Badari Pulavarty  <pbadari@linux.vnet.ibm.com>
>> Cc: Paul Mackerras <paulus@samba.org>
>> Cc: David Gibson <david@gibson.dropbear.id.au>
>> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
>> ---
>> Changes:
>> v2:
>> * added PPC-specific ppc_get_vcpu_dt_id() and ppc_get_vcpu_by_dt_id()
>> * fixed kvm_arch_vcpu_id() to use ppc_get_vcpu_dt_id()
>> * fixed emulated XICS
>> * removed kvm_arch_vcpu_id() stub for non-KVM case
> 
> Not having non-PPC code in the patch is definitely a good sign!
> 
> Acked-by: Paolo Bonzini <pbonzini@redhat.com>


Heh. Mr. Graf has objections against v3 of this patch in another thread :)



-- 
Alexey