Hi,
> 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.
I tried the test with "cache=off" option, here is the result.
The number of issued I/Os
--------------------------------------------------------------------
| device | sda11 | sda12 |
| weight setting | 80% | 20% |
|----------------------------+-------------------+-------------------|
| KVM | I/Os | 5217 | 5623 |
| cache=off | ratio to total | 48.1% | 51.9% |
|-----------+----------------+-------------------+-------------------|
| KVM | I/Os | 4397 | 2902 |
| cache=on | ratio to total | 60.2% | 39.8% |
|-----------+----------------+-------------------+-------------------|
|local | I/Os | 5447 | 1314 |
| | ratio to total | 80.6% | 19.4% |
--------------------------------------------------------------------
I could see the page cache effect through the /sys/block/sda/sda[12]/stat,
O_DIRECT was taking effect. However, the bandwidth control didn't work.
I also did another test. The difference from the previous test is that
the weights were assigned on a per partition basis instead of a per
cgroup basis.
It worked fine on Xen and local processes, but unfortunately it didn't
work on KVM.
The number of issued I/Os
The weights were assigned on a per partition basis
--------------------------------------------------------------------
| device | sda11 | sda12 |
| weight setting | 80% | 20% |
|----------------------------+-------------------+-------------------|
| KVM | I/Os | 5905 | 5873 |
| cache=off | ratio to total | 50.1% | 49.9% |
|-----------+----------------+-------------------+-------------------|
|local | I/Os | 6929 | 1629 |
| | ratio to total | 81.0% | 19.0% |
|--------------------------------------------------------------------|
| Xen | I/Os | 8534 | 2360 |
| | ratio to total | 78.3% | 21.7% |
--------------------------------------------------------------------
I don't understand what was going on. I'd be appreciate if you could give
me other suggestions.
Thanks,
Ryo Tsuruta
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