[ Reviving old thread. ]

Andrew Murray [off-list ref] writes:

On Tue, Nov 20, 2018 at 10:31:36PM +1100, Michael Ellerman wrote:

quoted

Andrew Murray [off-list ref] writes:

quoted

Update design.txt to reflect the presence of the exclude_host
and exclude_guest perf flags.

Signed-off-by: Andrew Murray <redacted>
---
 tools/perf/design.txt | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/perf/design.txt b/tools/perf/design.txt
index a28dca2..7de7d83 100644
--- a/tools/perf/design.txt
+++ b/tools/perf/design.txt

@@ -222,6 +222,10 @@ The 'exclude_user', 'exclude_kernel' and 'exclude_hv' bits provide a
 way to request that counting of events be restricted to times when the
 CPU is in user, kernel and/or hypervisor mode.
 
+Furthermore the 'exclude_host' and 'exclude_guest' bits provide a way
+to request counting of events restricted to guest and host contexts when
+using virtualisation.

How does exclude_host differ from exclude_hv ?

I believe exclude_host / exclude_guest are intented to distinguish
between host and guest in the hosted hypervisor context (KVM).

OK yeah, from the perf-list man page:

           u - user-space counting
           k - kernel counting
           h - hypervisor counting
           I - non idle counting
           G - guest counting (in KVM guests)
           H - host counting (not in KVM guests)

Whereas exclude_hv allows to distinguish between guest and
hypervisor in the bare-metal type hypervisors.

Except that's exactly not how we use them on powerpc :)

We use exclude_hv to exclude "the hypervisor", regardless of whether
it's KVM or PowerVM (which is a bare-metal hypervisor).

We don't use exclude_host / exclude_guest at all, which I guess is a
bug, except I didn't know they existed until this thread.

eg, in a KVM guest:

  $ perf record -e cycles:G /bin/bash -c "for i in {0..100000}; do :;done"
  $ perf report -D | grep -Fc "dso: [hypervisor]"
  16

In the case of arm64 - if VHE extensions are present then the host
kernel will run at a higher privilege to the guest kernel, in which
case there is no distinction between hypervisor and host so we ignore
exclude_hv. But where VHE extensions are not present then the host
kernel runs at the same privilege level as the guest and we use a
higher privilege level to switch between them - in this case we can
use exclude_hv to discount that hypervisor role of switching between
guests.

I couldn't find any arm64 perf code using exclude_host/guest at all?

And I don't see any x86 code using exclude_hv.

But maybe that's OK, I just worry this is confusing for users.

cheers

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