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[Qemu-discuss] Virtio-9p and cgroup io-throttling

From: Pradeep Kiruvale
Subject: [Qemu-discuss] Virtio-9p and cgroup io-throttling
Date: Thu, 7 Apr 2016 11:48:27 +0200

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?

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?


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