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From: | Anthony Liguori |
Subject: | Re: [Qemu-devel] [RFC]QEMU disk I/O limits |
Date: | Tue, 31 May 2011 17:22:13 -0500 |
User-agent: | Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110424 Lightning/1.0b2 Thunderbird/3.1.10 |
On 05/31/2011 03:48 PM, Mike Snitzer wrote:
On Tue, May 31 2011 at 2:39pm -0400, Anthony Liguori<address@hidden> 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
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