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Date:   Sun, 5 Jan 2020 06:25:59 -0500
From:   "Michael S. Tsirkin" <>
To:     Jason Wang <>
Cc:     "Liu, Jiang" <>,
        "Liu, Jing2" <>,
        Zha Bin <>,,,,,
Subject: Re: [virtio-dev] Re: [PATCH v1 2/2] virtio-mmio: add features for
 virtio-mmio specification version 3

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.


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