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SubjectRe: [virtio-dev] Re: [PATCH v1 2/2] virtio-mmio: add features for virtio-mmio specification version 3

On 2020/1/5 下午7:25, Michael S. Tsirkin wrote:
> On Fri, Jan 03, 2020 at 05:12:38PM +0800, Jason Wang wrote:
>> On 2020/1/3 下午2:14, Liu, Jiang wrote:
>>>> Ok, I get you now.
>>>> But still, having fixed number of MSIs is less flexible. E.g:
>>>> - for x86, processor can only deal with about 250 interrupt vectors.
>>>> - driver may choose to share MSI vectors [1] (which is not merged but we will for sure need it)
>>> Thanks for the info:)
>>> X86 systems roughly have NCPU * 200 vectors available for device interrupts.
>>> The proposed patch tries to map multiple event sources to an interrupt vector, to avoid running out of x86 CPU vectors.
>>> Many virtio mmio devices may have several or tens of event sources, and it’s rare to have hundreds of event sources.
>>> So could we treat the dynamic mapping between event sources and interrupt vectors as an advanced optional feature?
>> Maybe, but I still prefer to implement it if it is not too complex. Let's
>> see Michael's opinion on this.
>> Thanks
> I think a way for the device to limit # of vectors in use by driver is
> useful. But sharing of vectors doesn't really need any special
> registers, just program the same vector for multiple Qs/interrupts.

Right, but sine the #vectors is limited, we still need dynamic mapping
like what is done in PCI.



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