On Tue, Apr 4, 2017 at 5:56 PM, Will Deacon <will.dea...@arm.com> wrote: > On Tue, Apr 04, 2017 at 05:37:10PM +0530, Ganapatrao Kulkarni wrote: >> On Tue, Apr 4, 2017 at 4:48 PM, Will Deacon <will.dea...@arm.com> wrote: >> > On Tue, Apr 04, 2017 at 04:10:55PM +0530, Ganapatrao Kulkarni wrote: >> >> commit d98ecda (arm64: perf: Count EL2 events if the kernel is running in >> >> HYP) >> >> is returning error for perf syscall with mixed attribute set for >> >> exclude_kernel >> >> and exlude_hv. >> >> >> >> This change is breaking some applications (observed with hhvm) when >> >> ran with VHE enabled. Adding change to enable EL2 event counting, >> >> if either of or both of exclude_kernel and exlude_hv are not set. >> >> >> >> Signed-off-by: Ganapatrao Kulkarni <ganapatrao.kulka...@cavium.com> >> >> --- >> >> arch/arm64/kernel/perf_event.c | 19 ++++++++++++------- >> >> 1 file changed, 12 insertions(+), 7 deletions(-) >> > >> > Hmm. When we have VHE, we can't distinguish between hypervisor and kernel, >> > so this patch doesn't seem right to me. The code currently requires >> > both exclude_kernel and exclude_hv to be clear before we enable profiling >> > EL2, otherwise we're failing to exclude samples that were asked to be >> > excluded. >> >> The application cant differentiate that kernel is running in EL2/VHE or in >> EL1 >> when VHE=1, is it makes sense to enable EL2 event counting when there >> is request from application to either include kernel or hypervisor >> event count, since both are same. > > You can make exactly the same argument against your proposal by saying that > it makes sense to disable EL2 event counting when there is a request from > an application to either exclude kernel or hypervisor event counting.
yes, the argument is equally valid on either side. > >> IMO, it is not appropriate to have different application behaviour >> when kernel booted with VHE=0/1 > > Then find another solution to that. How about a mechanism to advertise > that exclude_hv is effectively always set if the kernel is running at EL2? I am not sure, how we can advertise to user that kernel is running at EL2. we may add a note to man page of perf_event_open? "exclude_hv is always set, if host kernel and hypervisor are running at same privilege level", > > That would mean that you would use exclude_kernel to determine the profiling > controls for the host. yes, this seems to be more appropriate. > > Will thanks Ganapat
