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Re: [Xen-users] perf hardware event on ARM64
On Friday, October 23, 2015, Ian Campbell <ian.campbell@xxxxxxxxxx> wrote:
On Fri, 2015-10-23 at 10:21 -0400, Jintack Lim wrote:
> 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?
You'd probably also need to adjust whichever register it is which causes
these accesses to be trapped to Xen.
> In my environment, I pinned vcpus of Dom0 and DomU on different set of physical cores,
> so there will be no context switch (except switching to idle domain)
OK. (although performance data from such a non-default configuration is
necessarily going to come with certain caveats)
BTW, any reason you aren't running 4.6 for this?
All my experiments are based on 4.5 which was the latest version at that time. That's the only reason. Â
Ian.
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