On Tue, Jan 08, 2019 at 11:36:33AM -0500, Boris Ostrovsky wrote:

On 1/8/19 5:48 AM, Peter Zijlstra wrote:

quoted

On the various exclude options; they are as follows (IIUC):

  - exclude_guest: we're a HV/host-kernel and we don't want the counter
                   to run when we run a guest context.

  - exclude_host: we're a HV/host-kernel and we don't want the counter
                  to run when we run in host context.

  - exclude_hv: we're a guest and don't want the counter to run in HV
                context.

Now, KVM always implies exclude_hv afaict (for guests), I'm not sure
what, if anything Xen does on x86 (IIRC Brendan Gregg once said perf
works on Xen) -- nor quite sure who to ask, Boris, Jeurgen?

perf does work inside guests.

VPMU is managed by the Xen and it presents to the guest only samples
that are associated with the guest. So from that perspective exclude_hv
doesn't seem to be needed.

There is a VPMU mode that allows profiling whole system (host and
guests) from dom0, and this where exclude_hv might be useful. But this
mode, ahem, needs some work.

Thanks Boris!

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