Subject: Re: [PATCH v4 10/13] x86: perf/core: use PERF_PMU_CAP_NO_EXCLUDE for exclude incapable PMUs

From: Peter Zijlstra <[email-masked]>
Date: Tue, 8 Jan 2019 11:48:41 +0100

On Mon, Jan 07, 2019 at 04:27:27PM +0000, Andrew Murray wrote:
> For drivers that do not support context exclusion let's advertise the
> PERF_PMU_CAP_NOEXCLUDE capability. This ensures that perf will
> prevent us from handling events where any exclusion flags are set.
> Let's also remove the now unnecessary check for exclusion flags.
> 
> Signed-off-by: Andrew Murray <[email-masked]>
> ---
>  arch/x86/events/amd/ibs.c          | 13 +------------
>  arch/x86/events/amd/power.c        | 10 ++--------
>  arch/x86/events/intel/cstate.c     | 12 +++---------
>  arch/x86/events/intel/rapl.c       |  9 ++-------
>  arch/x86/events/intel/uncore_snb.c |  9 ++-------
>  arch/x86/events/msr.c              | 10 ++--------
>  6 files changed, 12 insertions(+), 51 deletions(-)

You (correctly) don't add CAP_NO_EXCLUDE to the main x86 pmu code, but
then you also don't check if it handles all the various exclude options
correctly/consistently.

Now; I must admit that that is a bit of a maze, but I think we can at
least add exclude_idle and exclude_hv fails in there, nothing uses those
afaict.

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?