Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933444Ab2JXMgW (ORCPT ); Wed, 24 Oct 2012 08:36:22 -0400 Received: from mail-lb0-f174.google.com ([209.85.217.174]:55680 "EHLO mail-lb0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758522Ab2JXMgV (ORCPT ); Wed, 24 Oct 2012 08:36:21 -0400 MIME-Version: 1.0 In-Reply-To: <20121024123124.GU2095@tassilo.jf.intel.com> References: <1351058350-9159-1-git-send-email-zheng.z.yan@intel.com> <1351058350-9159-7-git-send-email-zheng.z.yan@intel.com> <5087CF96.7010406@intel.com> <5087D678.1080905@intel.com> <20121024123124.GU2095@tassilo.jf.intel.com> Date: Wed, 24 Oct 2012 14:36:19 +0200 Message-ID: Subject: Re: [PATCH V2 6/7] perf, x86: Use LBR call stack to get user callchain From: Stephane Eranian To: Andi Kleen Cc: "Yan, Zheng" , LKML , Peter Zijlstra Content-Type: text/plain; charset=UTF-8 X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1551 Lines: 37 On Wed, Oct 24, 2012 at 2:31 PM, Andi Kleen wrote: > On Wed, Oct 24, 2012 at 02:21:43PM +0200, Stephane Eranian wrote: >> But still, if I do: >> $ perf record -g -e cpu/cycles/k ........ >> >> Looks like your code will activate LBR cstack for user stack even >> though I don't use it. >> I know it won't generate any user samples (theoretically) but you are >> still commandeering >> the LBR resource which other events may want to use. > > You can disable it in sysfs. LBR is a power user feature and they will > know how to do this. > But isn't the whole point of the patch to hide LBR cstack from users so they won't know they're using it for user cstack? To disable it in sysfs, I need to know it's being used in the first place. You're saying, I need to know it is used only for user cstack and if I don't need it then I need to disable it explicitly. I also suspect using it for nothing may have some performance implication because you are saving/restoring on ctxsw, for instance. I think in x86_pmu_hw_config(), you could simply check the priv level restrictions on the event. If exclude_user is set, then don't active LBR cstack and that's it. That's what I was trying to get to... > See it as a "prefer the needs of the 95+% over the needs of the few" default > > -Andi -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/