Re: [Qemu-devel] Virtio-9p and cgroup io-throttling

[Pradeep Kiruvale <pradeepkiruvale@gmail.com>]

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Hi Greg,

Thanks for your reply.

Below is the way how I add to blkio

echo "8:16 8388608" >
/sys/fs/cgroup/blkio/test/blkio.throttle.write_bps_device

The problem I guess is adding these task ids to the "tasks" file in cgroup

These threads are started randomly and even then I add the PIDs to the
tasks file the cgroup still does not do IO control.

Is it possible to reduce these number of threads? I see different number of
threads doing IO at different runs.

Regards,
Pradeep


On 8 April 2016 at 10:10, Greg Kurz <gkurz@linux.vnet.ibm.com> wrote:

> On Thu, 7 Apr 2016 11:48:27 +0200
> Pradeep Kiruvale <pradeepkiruvale@gmail.com> wrote:
>
> > Hi All,
> >
> > I am using virtio-9p for sharing the file between host and guest. To test
> > the shared file I do read/write options in the guest.To have controlled
> io,
> > I am using cgroup blkio.
> >
> > While using cgroup I am facing two issues,Please find the issues below.
> >
> > 1. When I do IO throttling using the cgroup the read throttling works
> fine
> > but the write throttling does not wok. It still bypasses these throttling
> > control and does the default, am I missing something here?
> >
>
> Hi,
>
> Can you provide details on your blkio setup ?
>
> > I use the following commands to create VM, share the files and to
> > read/write from guest.
> >
> > *Create vm*
> > qemu-system-x86_64 -balloon none .......-name vm0 -cpu host -m 128 -smp 1
> > -enable-kvm -parallel .... -fsdev
> > local,id=sdb1,path=/mnt/sdb1,security_model=none,writeout=immediate
> -device
> > virtio-9p-pci,fsdev=sdb1,mount_tag=sdb1
> >
> > *Mount file*
> > mount -t 9p -o trans=virtio,version=9p2000.L sdb1 /sdb1_ext4 2>>dd.log &&
> > sync
> >
> > touch /sdb1_ext4/dddrive
> >
> > *Write test*
> > dd if=/dev/zero of=/sdb1_ext4/dddrive bs=4k count=800000 oflag=direct >>
> > dd.log 2>&1 && sync
> >
> > *Read test*
> > dd if=/sdb1_ext4/dddrive of=/dev/null >> dd.log 2>&1 && sync
> >
> > 2. The other issue is when I run "dd" command inside guest  it creates
> > multiple threads to write/read. I can see those on host using iotop is
> this
> > expected behavior?
> >
>
> Yes. QEMU uses a thread pool to handle 9p requests.
>
> > Regards,
> > Pradeep
>
> Cheers.
>
> --
> Greg
>
>

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