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Re: [Qemu-devel] [RFC]QEMU disk I/O limits
From: |
Sasha Levin |
Subject: |
Re: [Qemu-devel] [RFC]QEMU disk I/O limits |
Date: |
Thu, 02 Jun 2011 09:17:06 +0300 |
Hi,
On Mon, 2011-05-30 at 13:09 +0800, Zhi Yong Wu wrote:
> Hello, all,
>
> I have prepared to work on a feature called "Disk I/O limits" for
> qemu-kvm projeect.
> This feature will enable the user to cap disk I/O amount performed by a
> VM.It is important for some storage resources to be shared among multi-VMs.
> As you've known, if some of VMs are doing excessive disk I/O, they will hurt
> the performance of other VMs.
>
> More detail is available here:
> http://wiki.qemu.org/Features/DiskIOLimits
>
> 1.) Why we need per-drive disk I/O limits
> As you've known, for linux, cgroup blkio-controller has supported I/O
> throttling on block devices. More importantly, there is no single mechanism
> for disk I/O throttling across all underlying storage types (image file, LVM,
> NFS, Ceph) and for some types there is no way to throttle at all.
>
> Disk I/O limits feature introduces QEMU block layer I/O limits together
> with command-line and QMP interfaces for configuring limits. This allows I/O
> limits to be imposed across all underlying storage types using a single
> interface.
>
> 2.) How disk I/O limits will be implemented
> QEMU block layer will introduce a per-drive disk I/O request queue for
> those disks whose "disk I/O limits" feature is enabled. It can control disk
> I/O limits individually for each disk when multiple disks are attached to a
> VM, and enable use cases like unlimited local disk access but shared storage
> access with limits.
> In mutliple I/O threads scenario, when an application in a VM issues a
> block I/O request, this request will be intercepted by QEMU block layer, then
> it will calculate disk runtime I/O rate and determine if it has go beyond its
> limits. If yes, this I/O request will enqueue to that introduced queue;
> otherwise it will be serviced.
>
> 3.) How the users enable and play with it
> QEMU -drive option will be extended so that disk I/O limits can be
> specified on its command line, such as -drive [iops=xxx,][throughput=xxx] or
> -drive [iops_rd=xxx,][iops_wr=xxx,][throughput=xxx] etc. When this argument
> is specified, it means that "disk I/O limits" feature is enabled for this
> drive disk.
> The feature will also provide users with the ability to change per-drive
> disk I/O limits at runtime using QMP commands.
I'm wondering if you've considered adding a 'burst' parameter -
something which will not limit (or limit less) the io ops or the
throughput for the first 'x' ms in a given time window.
> Regards,
>
> Zhiyong Wu
>
--
Sasha.