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

[Pradeep Kiruvale <pradeepkiruvale@gmail.com>]

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Hi Greg,

FInd my replies inline

>
> > Below is the way how I add to blkio
> >
> > echo "8:16 8388608" >
> > /sys/fs/cgroup/blkio/test/blkio.throttle.write_bps_device
> >
>
> Ok, this just puts a limit of 8MB/s when writing to /dev/sdb for all
> tasks in the test cgroup... but what about the tasks themselves ?
>
> > The problem I guess is adding these task ids to the "tasks" file in
> cgroup
> >
>
> Exactly. :)
>
> > These threads are started randomly and even then I add the PIDs to the
> > tasks file the cgroup still does not do IO control.
> >
>
> How did you get the PIDs ? Are you sure these threads you have added to the
> cgroup are the ones that write to /dev/sdb ?
>

*Yes, I get PIDs from /proc/Qemu_PID/task*



>
> > Is it possible to reduce these number of threads? I see different number
> of
> > threads doing IO at different runs.
> >
>
> AFAIK, no.
>
> Why don't you simply start QEMU in the cgroup ? Unless I miss something,
> all
> children threads, including the 9p ones, will be in the cgroup and honor
> the
> throttle setttings.
>


*I started the qemu with cgroup as below*

*cgexec -g blkio:/test qemu.......*
*Is there any other way of starting the qemu in cgroup?*

Regards,
Pradeep


>
> > Regards,
> > Pradeep
> >
>
> Cheers.
>
> --
> Greg
>
> >
> > 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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