[Qemu-devel] Tracking the VM making an IO request

[Qemu-devel] Tracking the VM making an IO request

[Aarian P. Aleahmad]

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Hi there

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.

Sincerely Yours,
Aarian

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Re: [Qemu-devel] Tracking the VM making an IO request

[Stefan Hajnoczi]

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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.

Finally, if you prefer you could set up an iSCSI or NBD target and
simply use Wireshark to record and analyze the I/O request patterns.

Stefan

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Re: [Qemu-devel] Tracking the VM making an IO request

[Paolo Bonzini]

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

Re: [Qemu-devel] Tracking the VM making an IO request

[Aarian P. Aleahmad]

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Thanks for helping me. what should I do in case of using KVM?

On Wed, Feb 10, 2016 at 4:10 PM, Paolo Bonzini <pbonzini@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
>

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Re: [Qemu-devel] Tracking the VM making an IO request

[Fam Zheng]

On Sat, 03/12 16:17, Aarian P. Aleahmad wrote:
> Thanks for helping me. what should I do in case of using KVM?

The said method works exactly the same with or without -enable-kvm.

Fam

> 
> On Wed, Feb 10, 2016 at 4:10 PM, Paolo Bonzini <pbonzini@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
> >