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Re: [Qemu-devel] [PATCH V1 1/1] arm64: Add an option to turn on/off host
From: |
Andrea Bolognani |
Subject: |
Re: [Qemu-devel] [PATCH V1 1/1] arm64: Add an option to turn on/off host-backed vPMU support |
Date: |
Mon, 15 Aug 2016 19:24:38 +0200 |
On Mon, 2016-08-15 at 11:12 -0500, Wei Huang wrote:
> > Did you already try driving this with libvirt? It should work
> > out of the box.
> >
> > If you haven't, I will do it :)
>
> No, I haven't. All tests were done based on command line to QEMU. :-)
Fair enough :)
I did some testing on my own using libvirt to drive a QEMU
binary that included your patch, and it looks like everything
is working as expected: if I turn PMU on using the appropriate
XML element (<pmu state='on'/>) I can access the performance
counters from inside the guest; if I disable it explicitly or
don't enable it, I can't.
The host-side testing involved making sure the 'pmu' flag
was passed, or not passed, to QEMU and the value, if any,
matched the guest XML.
The guest-side testing involved running
$ dmesg | grep -i pmu
$ perf list | grep 'Hardware event'
and making sure some output was returned in both cases, and
making sure the 'instructions' counter was not marked as '<not
supported>' in the output of
$ perf stat true
If the kind of testing I performed is not good enough, please
let me know and I'll do another round.
This was tested only with <cpu mode='host-passthrough'/> (the
libvirt equivalent of -cpu host), because the aarch64 CPU
driver in libvirt is not currently capable of handling other
CPU models for KVM guests.
I also verified that TCG guests didn't accept the 'pmu' flag.
--
Andrea Bolognani / Red Hat / Virtualization