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

[Pradeep Kiruvale <pradeepkiruvale@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 4947 bytes --]

Hi Greg,

Yes, it was nothing to do with the virtio-9p. I was writing at 4k Blocks
now I changed it to 1K Block. This works fine for me.

Thanks for your help.

Regards,
Pradeep

On 8 April 2016 at 16:58, Greg Kurz <gkurz@linux.vnet.ibm.com> wrote:

> On Fri, 8 Apr 2016 14:55:29 +0200
> Pradeep Kiruvale <pradeepkiruvale@gmail.com> wrote:
>
> > 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*
> >
>
> And then you echoed the PIDs to /sys/fs/cgroup/blkio/test/tasks ?
>
> This is racy... another IO thread may be started to do some work on
> /dev/sdb
> just after you've read PIDs from /proc/Qemu_PID/task, and it won't be part
> of the cgroup.
>
> >
> >
> > >
> > > > 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?*
> >
>
> Maybe you can pass --sticky to cgexec to prevent cgred from moving
> children tasks to other cgroups...
>
> There's also the old fashion method:
>
> # echo $$ > /sys/fs/cgroup/blkio/test/tasks
> # qemu.....
>
> This being said, QEMU is a regular userspace program that is completely
> cgroup
> agnostic. It won't behave differently than 'dd if=/dev/sdb of=/dev/null'.
>
> This really doesn't look like a QEMU related issue to me.
>
> > Regards,
> > Pradeep
> >
>
> Cheers.
>
> --
> Greg
>
> >
> > >
> > > > 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
> > > > >
> > > > >
> > >
> > >
>
>
>

[-- Attachment #2: Type: text/html, Size: 7562 bytes --]