Re: [Xen-users] perf hardware event on ARM64

[Jintack Lim <jintack@xxxxxxxxxxxxxxx>]

Thanks Ian.

On Fri, Oct 23, 2015 at 9:44 AM, Ian Campbell <ian.campbell@xxxxxxxxxx> wrote:

On Fri, 2015-10-23 at 09:22 -0400, Jintack Lim wrote:
> Hi,
>
> I'm working on ARM64 (AppliedMicroâ X-Gene).
> I wanted to run perf to collect some hardware events, but I got some
> trouble.
> Basically I have two questions.
>
> 1.
> I found that pmu is not registered in the device tree,
> while it is registered on native linux (installed on the same type of
> machine) .
> Can I just modify device tree at booting time to make it look like native
> linux?
> Will it work?

> Additional information is at the bottom.
>
> 2.
> I found that running perf on Xen 4.5.0 resulted in segmentation fault (or
> system crash),
> however it runs well on the latest Xen on git server.
> Can somebody point the patch that makes this change?

4.5.0 was vulnerable to XSA-93:

http://xenbits.xen.org/xsa/advisory-93.html

The core issue with PMU is that Xen currently does not know how to context
switch the relevant state when changing guests. Fixing that would be more
work than just fiddling with device tree.

So, if we don't worry about the context switching, then modifying device tree will just work?

In my environment, I pinned vcpus of Dom0 and DomU on different set of physical cores,Â

so there will be no context switch (except switching to idle domain)

Â

You might be able to bodge something useful (but unsupported) together by
just allowing only dom0 to access these registers and to see the values
collected from the whole system (i.e. don't worry about context switching).
How useful such numbers would be depends somewhat on what you are hoping to
find out from this exercise.

Ok, I'll try.

Thank you so much again!Â

Ian.

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