Thanks for helping me. what should I do in case of using KVM? On Wed, Feb 10, 2016 at 4:10 PM, Paolo Bonzini <pbonz...@redhat.com> wrote:
> > > On 10/02/2016 11:23, Stefan Hajnoczi wrote: > > On Wed, Feb 10, 2016 at 12:35:54PM +0330, Aarian P. Aleahmad > > wrote: > >> I'm a student, engaged in a project in which QEMU is a candidate > >> to be used to make some studies about IO usage etc. I need to > >> track the IO requests made to the block devices (e.g. HDD, SSD, > >> etc.). I check the source code but I was confused. What I want to > >> know is that when an IO request is made, find out that which on > >> of the VMs has made that request. I'll thank you if you help me > >> on this issue. > > > > There are trace events that you can use. See docs/tracing.txt and > > trace-events. > > > > virtio_blk_handle_write and virtio_blk_handle_read can be used if > > your guest has virtio-blk. > > > > The QEMU block layer also has trace events named bdrv_aio_*. > > > > Or you could use blktrace(8) in the guest or on the host, depending > > on how you've set up storage. > > It's the third time I've gotten the question recently which makes me > believe the others were friends with Aarian... > > Each QEMU process represents a single VM. Therefore, it is simple to > answer the question "which VM is making the request"; the answer is > "the one for the QEMU process you are tracing". > > You probably want to use blktrace if you care about multiple VMs. > Alternatively, you can use tracing as mentioned by Stefan. If you > compile QEMU with --enable-trace-backend=simple, the resulting files > can be parsed with Python programs (see scripts/simpletrace.py). The > trace files include the pid and a timestamp based on CLOCK_MONOTONIC, > so it should be easy to merge the traces together. > > Paolo >
