[ Reviving old thread. ]
Andrew Murray <andrew.murray@xxxxxxx> writes:
> On Tue, Nov 20, 2018 at 10:31:36PM +1100, Michael Ellerman wrote:
>> Andrew Murray <andrew.murray@xxxxxxx> writes:
>>
>> > Update design.txt to reflect the presence of the exclude_host
>> > and exclude_guest perf flags.
>> >
>> > Signed-off-by: Andrew Murray <andrew.murray@xxxxxxx>
>> > ---
>> > 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
