Messages in this thread | | | From | Michael Ellerman <> | Subject | Re: [PATCH 10/10] perf/doc: update design.txt for exclude_{host|guest} flags | Date | Tue, 11 Dec 2018 22:06:53 +1100 |
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[ Reviving old thread. ]
Andrew Murray <andrew.murray@arm.com> writes: > On Tue, Nov 20, 2018 at 10:31:36PM +1100, Michael Ellerman wrote: >> Andrew Murray <andrew.murray@arm.com> writes: >> >> > Update design.txt to reflect the presence of the exclude_host >> > and exclude_guest perf flags. >> > >> > Signed-off-by: Andrew Murray <andrew.murray@arm.com> >> > --- >> > 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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