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Date: Fri, 8 Apr 2016 10:10:54 +0200
From: Greg Kurz <gkurz@linux.vnet.ibm.com>
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Subject: Re: [Qemu-devel] Virtio-9p and cgroup io-throttling
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To: Pradeep Kiruvale <pradeepkiruvale@gmail.com>
Cc: qemu-devel@nongnu.org, "qemu-discuss@nongnu.org" <qemu-discuss@nongnu.org>

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