Re: [Qemu-devel] [RFC][PATCH 23/45] qemu-kvm: Rework MSI-X mask notifier to generic MSI config notifiers

[Jan Kiszka]

On 2011-10-17 13:40, Michael S. Tsirkin wrote:
> On Mon, Oct 17, 2011 at 11:27:57AM +0200, Jan Kiszka wrote:
>> MSI config notifiers are supposed to be triggered on every relevant
>> configuration change of MSI vectors or if MSI is enabled/disabled.
>>
>> Two notifiers are established, one for vector changes and one for general
>> enabling. The former notifier additionally passes the currently active
>> MSI message.
>> This will allow to update potential in-kernel IRQ routes on
>> changes. The latter notifier is optional and will only be used by a
>> subset of clients.
>>
>> These notifiers are currently only available for MSI-X but will be
>> extended to legacy MSI as well.
>>
>> Signed-off-by: Jan Kiszka <address@hidden>
> 
> Passing message, always, does not seem to make sense: message is only
> valid if it is unmasked.

If we go from unmasked to masked, the consumer could just ignore the
message.

> Further, IIRC the spec requires any changes to be done while
> message is masked. So mask notifier makes more sense to me:
> it does the same thing using one notifier that you do
> using two notifiers.

That's in fact a possible optimization (only invoke the callback on mask
transitions). Not sure if that applies to MSI as well, probably not. To
have common types, I would prefer to stay with vector config notifiers
as name then.

Jan

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