[dm-devel] Re: I/O bandwidth control on KVM

[Avi Kivity]

Anthony Liguori wrote:
> Hi Ryo,
>
> Ryo Tsuruta wrote:
>   
>> Hello all,
>>
>> I've implemented a block device which throttles block I/O bandwidth, 
>> which I called dm-ioband, and been trying to throttle I/O bandwidth on
>> KVM environment. But unfortunately it doesn't work well, the number of
>> issued I/Os is not according to the bandwidth setting.
>> On the other hand, I got the good result when accessing directly to
>> the local disk on the local machine.
>>
>> I'm not so familiar with KVM. Could anyone give me any advice?
>>     
>
> If you are using virtio drivers in the guest (which I presume you are 
> given the reference to /dev/vda), try using the following -drive syntax:
>
> -drive file=/dev/mapper/ioband1,if=virtio,boot=on,cache=off
>
> This will force the use of O_DIRECT.  By default, QEMU does not open 
> with O_DIRECT so you'll see page cache effects.
>
>   

Good point.  But IIRC cache=off is not limited to virtio?


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