Re: [PATCH 10/10] perf/doc: update design.txt for exclude_{host|guest} flags

[Andrew Murray <andrew.murray@arm.com>]

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

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.

Thanks,

Andrew Murray

> 
> cheers