Re: [Xen-devel] Questions about Using Perf at Dom0

[Sanghyun Hong <shhong@xxxxxxx>]

Yes, this will allow the hypervisor to collect samples from multiple
guests. However, the tool (perf) probably won't be able to properly
process these samples. But you can try.

I understand, thus, I applied the patches and set the pmu_mode to all. However, I’m really curious what you mean by the tool (perf) probably won’t be able to properly process these samples. Is there any things I have to have in mind while collecting the counters, or will it have incorrect values of the counters?

You will want to run dom0 on all physical processors (i.e. no
dom0_max_vcpus boot option) and pin all VCPUs for both dom0 and the guest.

Sure, thanks! My machine has four physical cores, and I’ve set the dom0_max_vcpus=4. I think it will have the same effect in removing the dom0_max_vcpus option.

Best,

Sanghyun.

On Aug 29, 2016, at 4:59 PM, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> wrote:

On 08/29/2016 02:42 PM, Sanghyun Hong wrote:

Hi Boris,

I’ve found the
documentations(https://github.com/torvalds/linux/blob/master/Documentation/ABI/testing/sysfs-hypervisor-pmu)
in the kernel source code, and it seems like if we change the mode
from *self* to *all* then we can collect counters for all the domains,
right?

Yes, this will allow the hypervisor to collect samples from multiple
guests. However, the tool (perf) probably won't be able to properly
process these samples. But you can try.

You will want to run dom0 on all physical processors (i.e. no
dom0_max_vcpus boot option) and pin all VCPUs for both dom0 and the guest.


-boris

All the best,
Sanghyun.

On Aug 29, 2016, at 12:36 PM, Boris Ostrovsky
<boris.ostrovsky@xxxxxxxxxx <mailto:boris.ostrovsky@xxxxxxxxxx>> wrote:

On 08/29/2016 09:18 AM, Sanghyun Hong wrote:

Dear Xen-Devel Community:

I’m a grad student working on measuring performance counters at the
Xen domains. I read this
thread(https://wiki.xenproject.org/wiki/Xen_Profiling:_oprofile_and_perf)
in
web, and it says using Linux perf command will let us collecting
performance counters in both dom0 and domU. Does it mean that we can
collect both of them at once if we run perf command on the dom0? (If
not, does it mean we can collect counters for each domain separately
once we run the perf command in each domain?

Profiling both guest and dom0 (and the hypervisor) requires changes to
perf and those are not there yet.

But you can run perf in each guest (including dom0) separately. Make
sure you have vpmu=true boot option.

-boris

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel