Re: [Qemu-devel] [RFC]QEMU disk I/O limits

[Anthony Liguori <anthony@codemonkey.ws>]

On 05/31/2011 03:48 PM, Mike Snitzer wrote:
> On Tue, May 31 2011 at  2:39pm -0400,
> Anthony Liguori<anthony@codemonkey.ws>  wrote:
>
>>> Are you referring to merging taking place which can change the definition
>>> of IOPS as seen by guest?
>>
>> No, with qcow2, it may take multiple real IOPs for what the guest
>> sees as an IOP.
>>
>> That's really the main argument I'm making here.  The only entity
>> that knows what a guest IOP corresponds to is QEMU.  On the backend,
>> it may end up being a network request, multiple BIOs to physical
>> disks, file access, etc.
>
> Couldn't QEMU give a hint to the kernel about the ratio of guest IOP to
> real IOPs?  Or is QEMU blind to the real IOPs that correspond to a guest
> IOP?

Perhaps, but how does that work when the disk image is backed by NFS?

And even if you had a VFS level API, we can do things like libcurl based 
block devices in QEMU.  So unless you tried to do level 5 traffic 
throttling which hopefully, you'll agree is total overkill, we're going 
to need to have this functionality in QEMU no matter what.

Regards,

Anthony Liguori