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Re: [Qemu-devel] Using PCI config space to indicate config location
From: |
Gerd Hoffmann |
Subject: |
Re: [Qemu-devel] Using PCI config space to indicate config location |
Date: |
Mon, 08 Oct 2012 22:13:37 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:10.0.7) Gecko/20120825 Thunderbird/10.0.7 |
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.
cheers,
Gerd
- 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 <=
- 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, 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