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Re: [Qemu-devel] Using PCI config space to indicate config location
From: |
Anthony Liguori |
Subject: |
Re: [Qemu-devel] Using PCI config space to indicate config location |
Date: |
Mon, 08 Oct 2012 15:55:44 -0500 |
User-agent: |
Notmuch/0.13.2+93~ged93d79 (http://notmuchmail.org) Emacs/23.3.1 (x86_64-pc-linux-gnu) |
Gerd Hoffmann <address@hidden> writes:
> Hi,
>
>>> So we could have for virtio something like this:
>>>
>>> Capabilities: [??] virtio-regs:
>>> legacy: BAR=0 offset=0
>>> virtio-pci: BAR=1 offset=1000
>>> virtio-cfg: BAR=1 offset=1800
>>
>> This would be a vendor specific PCI capability so lspci wouldn't
>> automatically know how to parse it.
>
> Sure, would need a patch to actually parse+print the cap,
> /me was just trying to make my point clear in a simple way.
>
>>>>> 2) ISTR an argument about mapping the ISR register separately, for
>>>>> performance, but I can't find a reference to it.
>>>>
>>>> I think the rationale is that ISR really needs to be PIO but everything
>>>> else doesn't. PIO is much faster on x86 because it doesn't require
>>>> walking page tables or instruction emulation to handle the exit.
>>>
>>> Is this still a pressing issue? With MSI-X enabled ISR isn't needed,
>>> correct? Which would imply that pretty much only old guests without
>>> MSI-X support need this, and we don't need to worry that much when
>>> designing something new ...
>>
>> It wasn't that long ago that MSI-X wasn't supported.. I think we should
>> continue to keep ISR as PIO as it is a fast path.
>
> No problem if we allow to have both legacy layout and new layout at the
> same time. Guests can continue to use ISR @ BAR0 in PIO space for
> existing virtio devices, even in case they want use mmio for other
> registers -> all fine.
>
> New virtio devices can support MSI-X from day one and decide to not
> expose a legacy layout PIO bar.
I think having BAR1 be an MMIO mirror of the registers + a BAR2 for
virtio configuration space is probably not that bad of a solution.
Regards,
Anthony Liguori
>
> cheers,
> Gerd
>
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- Re: [Qemu-devel] Proposal for virtio standardization., Anthony Liguori, 2012/10/04
- [Qemu-devel] Using PCI config space to indicate config location, Rusty Russell, 2012/10/07
- Re: [Qemu-devel] Using PCI config space to indicate config location, Anthony Liguori, 2012/10/08
- Re: [Qemu-devel] Using PCI config space to indicate config location, Gerd Hoffmann, 2012/10/08
- Re: [Qemu-devel] Using PCI config space to indicate config location, Anthony Liguori, 2012/10/08
- Re: [Qemu-devel] Using PCI config space to indicate config location, Gerd Hoffmann, 2012/10/08
- Re: [Qemu-devel] Using PCI config space to indicate config location,
Anthony Liguori <=
- Re: [Qemu-devel] Using PCI config space to indicate config location, Rusty Russell, 2012/10/08
- Re: [Qemu-devel] Using PCI config space to indicate config location, Anthony Liguori, 2012/10/08
- Re: [Qemu-devel] Using PCI config space to indicate config location, Rusty Russell, 2012/10/08
- Re: [Qemu-devel] Using PCI config space to indicate config location, Avi Kivity, 2012/10/09
- Re: [Qemu-devel] Using PCI config space to indicate config location, Anthony Liguori, 2012/10/09
- Re: [Qemu-devel] Using PCI config space to indicate config location, Anthony Liguori, 2012/10/09
- Re: [Qemu-devel] Using PCI config space to indicate config location, Rusty Russell, 2012/10/10
- Re: [Qemu-devel] Using PCI config space to indicate config location, Michael S. Tsirkin, 2012/10/10
- Re: [Qemu-devel] Using PCI config space to indicate config location, Jamie Lokier, 2012/10/09
- Re: [Qemu-devel] Using PCI config space to indicate config location, Rusty Russell, 2012/10/10