Hi,

On 02/03/2012 06:59 AM, Mulyadi Santosa wrote:

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.

If I understand the patch which introduces the blk tracer to ftrace 
(http://lwn.net/Articles/315508/) just uses the blktrace interface. So I 
wonder why using this influences the I/O behaviour.

Best regards,
Matthias