Re: [Qemu-devel] On block interface types in general, IF_AHCI in particular

[Anthony Liguori <anthony@codemonkey.ws>]

Alexander Graf <agraf@suse.de> writes:

> On 31.10.2012, at 17:46, Anthony Liguori wrote:
>
>> Alexander Graf <agraf@suse.de> writes:
>> 
>> 
>> We had 11,286 hits from WinXP last month on qemu.org
>> 
>> Compare that to 16,716 hits for 64-bit Linux and a mere 9,516 hits for
>> 32-bit Linux.
>
> So how many hits is that for Mac OS X? That one only works with AHCI,
> but breaks with PIIX IDE.


2,661 for 10.7, 3,769 for 10.8.  These are the only versions you're even
allowed to run in a VM.  And given the other restrictions around running
Mac OS X guests, it's an even smaller audience.

>> WinXP is still an important guest.  And the real problem is that using
>> SATA is a catostrophic failure.  The guest won't install or boot at all.
>> 
>> And more to the point, AHCI performance is not very good anyway.  You
>> keep making assertions about how much better it is but I don't see data
>> to back that up (especially compared to where we're at with state of the
>> art virtio).
>
> I would really like to see good numbers on that. Performance certainly
> did degrade over time. The biggest issue I've see is that the
> in-kernel APIC always issues an ioctl on qemu_irq_lower() which
> happens a lot in cases where the line is already down. But I'd be more
> than happy to see some actual performance analysis of the matter.

Well until there's clear performance info, we should tone down the
assertions of how great AHCI performance is compared to IDE.  It's all
theoritical right now.

Breaking guests that work today and are widely used for a theoritical
performance improvement is not a reasonable path forward.

Regards,

Anthony Liguori

>
>
> Alex