Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753948AbdDDM0Q (ORCPT ); Tue, 4 Apr 2017 08:26:16 -0400 Received: from foss.arm.com ([217.140.101.70]:43768 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752814AbdDDM0P (ORCPT ); Tue, 4 Apr 2017 08:26:15 -0400 Date: Tue, 4 Apr 2017 13:26:32 +0100 From: Will Deacon To: Ganapatrao Kulkarni Cc: Ganapatrao Kulkarni , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , Catalin Marinas , Mark Rutland , Marc Zyngier , jnair@caviumnetworks.com Subject: Re: [PATCH] arm64: perf: Count EL2 events if either of kernel and hyp are not excluded Message-ID: <20170404122632.GF14898@arm.com> References: <1491302455-5939-1-git-send-email-ganapatrao.kulkarni@cavium.com> <20170404111826.GD14898@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1991 Lines: 41 On Tue, Apr 04, 2017 at 05:37:10PM +0530, Ganapatrao Kulkarni wrote: > On Tue, Apr 4, 2017 at 4:48 PM, Will Deacon 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 > >> --- > >> 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. > 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? That would mean that you would use exclude_kernel to determine the profiling controls for the host. Will