Re: [Qemu-devel] [RFC][PATCH 12/45] msi: Introduce MSIRoutingCache

[Jan Kiszka]

On 2011-10-17 13:06, Avi Kivity wrote:
> On 10/17/2011 11:27 AM, Jan Kiszka wrote:
>> This cache will help us implementing KVM in-kernel irqchip support
>> without spreading hooks all over the place.
>>
>> KVM requires us to register it first and then deliver it by raising a
>> pseudo IRQ line returned on registration. While this could be changed
>> for QEMU-originated MSI messages by adding direct MSI injection, we will
>> still need this translation for irqfd-originated messages. The
>> MSIRoutingCache will allow to track those registrations and update them
>> lazily before the actual delivery. This avoid having to track MSI
>> vectors at device level (like qemu-kvm currently does).
>>
>>
>> +typedef enum {
>> +    MSI_ROUTE_NONE = 0,
>> +    MSI_ROUTE_STATIC,
>> +} MSIRouteType;
>> +
>> +struct MSIRoutingCache {
>> +    MSIMessage msg;
>> +    MSIRouteType type;
>> +    int kvm_gsi;
>> +    int kvm_irqfd;
>> +};
>> +
>> diff --git a/hw/pci.h b/hw/pci.h
>> index 329ab32..5b5d2fd 100644
>> --- a/hw/pci.h
>> +++ b/hw/pci.h
>> @@ -197,6 +197,10 @@ struct PCIDevice {
>>      MemoryRegion rom;
>>      uint32_t rom_bar;
>>  
>> +    /* MSI routing chaches */
>> +    MSIRoutingCache *msi_cache;
>> +    MSIRoutingCache *msix_cache;
>> +
>>      /* MSI entries */
>>      int msi_entries_nr;
>>      struct KVMMsiMessage *msi_irq_entries;
> 
> IMO this needlessly leaks kvm information into core qemu.  The cache
> should be completely hidden in kvm code.
> 
> I think msi_deliver() can hide the use of the cache completely.  For
> pre-registered events like kvm's irqfd, you can use something like
> 
>   qemu_irq qemu_msi_irq(MSIMessage msg)
> 
> for non-kvm, it simply returns a qemu_irq that triggers a stl_phys();
> for kvm, it allocates an irqfd and a permanent entry in the cache and
> returns a qemu_irq that triggers the irqfd.

See my previously mail: you want to track the life-cycle of an MSI
source to avoid generating routes for identical sources. A messages is
not a source. Two identical messages can come from different sources. So
we need a separate data structure for that purpose.

Jan

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