blktrace vs ftrace

[Mulyadi Santosa]

Hi :)

On Fri, Feb 3, 2012 at 02:06, Matthias Brugger
<matthias.bgg at googlemail.com> wrote:
>
> qemu -hda scheduler.raw -drive
> file=/mnt/disk/testdisk2.img,if=virtio,cache=none -m 1024 -enable-kvm -k es
> -smp 2 -vnc 127.0.0.1:10 -smb /home/matthias/nfs/
>
>
> I use qemu-0.15.1 configured with the following parameter:
>
> ./configure --disable-xen re--enable-kvm --enable-io-thread
> --enable-vnc-thread --disable-darwin-user --disable-bsd-user
> --target-list=i386-softmmu

Looks like indeed you were seeing I/O threads from qemu kicks in.

I could only offer this explanation:
blktrace traces events in block level. In this level, I/O is likely
serialized....unless you have more than one physical disks.

in ftrace, you see events right before it hits block level operation.
Somewhere between VFS, filesystem operation and I/O scheduling which
deals with queue reordering. In this case, parallel operation is
likely to happen because more than processes could submit read or
write.

-- 
regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com