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



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?


--
error compiling committee.c: too many arguments to function


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