Re: [Qemu-devel] virtio-blk issues

[Avi Kivity <avi@redhat.com>]

Christoph Hellwig wrote:
> On Mon, Mar 16, 2009 at 03:22:24PM +0200, Avi Kivity wrote:
>   
>> The kvm bios supports 32 slots; I don't know if upstream bochs picked up 
>> these changes.
>>     
>
> I tried using the kvm pc-bios with upstream qemu, but it fails pretty
> early on when the kernel tries to initialize the timer interrupt.
>
>   

Interrupt routing is different between kvm and qemu due to HPET sending 
interrupts to PIC IRQ0 and IOAPIC INTI2; the kvm up to 2.6.29 only 
supports 1:1 mapping between PIC and IOAPIC pins 0-15.

> What's the protocol for syncing all those bios changes?
>   

I merge them occasionally, but in this case, syncing the changes would 
cause one or the other to break.

What is needed is to sync the qemu changes, and additionally add code to 
detect the non-existence of non-1:1 mapping and revert back to the old 
behavior in that case (and disable HPET as well).

>> In any case I'd like to see a virtio-blk controller which can support an 
>> arbitrary number of disks, much like a SCSI controller.  A pci slot or 
>> function per disk is wasteful.
>>     
>
> I'll see what I can do.
>   

Did I mention my wishlist includes indirect virtio requests, where a 
virtio ring entry points to an sglist instead of the buffer?  Right now 
a 1MB request will consume 256 ring entries, which kills concurrency 
with many disks on a single ring.

-- 
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