Hi Perf Maintainers, your suggestion on below discussion is much appreciated!
On Wed, Apr 5, 2017 at 2:01 PM, Will Deacon <will.dea...@arm.com> wrote: > On Wed, Apr 05, 2017 at 09:29:32AM +0530, Ganapatrao Kulkarni wrote: >> 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", > > I was thinking of putting something into sysfs, alongside the other things > we have in there. For example, a file that describes whether any of the > perf_event_attr behave as though they are fixed to a certain value. We > should involve the perf maintainers (and perf tool developers) in this, > but perhaps something like an attr directory, where we could have a file > called exclude_hv that contains the value 1. > > Will thanks Ganapat
