On Fri, Sep 02, 2011 at 08:34:19AM -0500, Adam Litke wrote:

From: Adam Litke <agl@us.ibm.com> To: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com> Cc: libvir-list@redhat.com Subject: Re: [libvirt] [RFC] block I/O throttling: how to enable in libvirt Message-ID: <20110902133419.GW15683@aglitke.rchland.ibm.com> References: <20110901050531.GB17963@f15.cn.ibm.com> <20110902021447.GD19143@f15.cn.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110902021447.GD19143@f15.cn.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Brightmail-Tracker: AAAAAA== X-Xagent-From: agl@us.ibm.com X-Xagent-To: wuzhy@linux.vnet.ibm.com X-Xagent-Gateway: vmsdvma.vnet.ibm.com (XAGENTU8 at VMSDVMA)

On Fri, Sep 02, 2011 at 10:14:48AM +0800, Zhi Yong Wu wrote:

...

On Thu, Sep 01, 2011 at 01:05:31PM +0800, Zhi Yong Wu wrote: HI, Adam, Now stefan, Daniel, and Gui all suggest extending blkiotune to keep libivrt unified interface. What do you think of it?

It seems like it would be nice to extend the blkiotune API for this use case, but there is one problem. The blkiotune interface operates at the VM level and the QEMU throttling is at the disk level. So if you want per-disk throttling granularity the blkiotune API may not be suitable. I see 3 possible paths forward:

1) Accept the blkiotune limitation of a global setting and add a throttle option that assigns the same throttle value to all disks.

<blkiotune> <shares>250</shares> <throttle>1024</throttle> </blkiotune>

+ Nice for simplicity and ease of implementation - May be too simplistic (can't set different throttling for different disks)

2) Extend the blkiotune API to allow per-disk tunings:

<blkiotune> <shares>250</shares> <throttle device='virtio-disk0'>1024</throttle> </blkiotune>

+ Use an existing API - Unfortunately it doesn't look like this can be done cleanly

3) Use a new API virDomainSetBlkDevParameters() to set device specific tuning parameters:

<blkiotune> <shares>250</shares> </blkiotune> ... <disk type='file' device='disk'> <driver name='qemu' type='raw'/> <source file='...'/> <target dev='vda' bus='virtio'/> <blkdevtune> <throttle>1024</throttle> Several I/O throttling tags should be supported, such as thrbps, thrbpsrd, thrbpswr, thriops, etc. </blkdevtune> </disk>

+ Throttle can be specified with the disk it is effecting - Proliferation of tuning APIs

Obviously #1 is the best if you can accept the limitations of the API. #2 would #1 is not accepted by us. If it is adopted, the advantage of QEMU I/O throttling is not used fully. be nice if we could figure out how to extend virTypedParameter to represent a I guess that #2 is less extendable than #3. (disk, param) pair. I see #3 as a last resort. Did I miss any other solutions. To be honest, i prefer to #3. At first, i plan to check how blkiotune works currently. Did I just manage to completely over-complicate this? :) NO, they are nice. thanks.

Regards, Zhiyong Wu

-- Adam Litke <agl@us.ibm.com> IBM Linux Technology Center