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Re: [Qemu-devel] [PATCH RFC 1/1] arm64: add an option to turn on/off vpm
From: |
Andrea Bolognani |
Subject: |
Re: [Qemu-devel] [PATCH RFC 1/1] arm64: add an option to turn on/off vpmu support |
Date: |
Mon, 01 Aug 2016 16:55:01 +0200 |
On Mon, 2016-08-01 at 14:32 +0100, Peter Maydell wrote:
> > Wouldn't that mean that you'd be unable to use
> >
> > -cpu foo,pmu=off
> >
> > if CPU model 'foo' doesn't support a PMU? I'd expect that
> > to work.
>
> The current precedent (has_el3) doesn't work like that: if
> foo isn't a CPU which can support EL3 then the property doesn't
> exist, and it's an error to try to set it.
Doesn't look like the pmu option works like that on x86,
though, unless I'm missing something.
I have a guest running with
-cpu pentium,pmu=on
and I can't see hardware perf events from inside the guest,
eg. dmesg reports
Performance Events: no PMU driver, software events only.
and perf tells me
<not supported> instructions
<not supported> branches
...
I'm not sure whether that's because the PMU is being
emulated but the kernel doesn't have a driver for it, or
whether it's not being emulated at all. Any way to find
out?
--
Andrea Bolognani / Red Hat / Virtualization