Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758463Ab2JXLdK (ORCPT ); Wed, 24 Oct 2012 07:33:10 -0400 Received: from mga01.intel.com ([192.55.52.88]:36317 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758266Ab2JXLdJ (ORCPT ); Wed, 24 Oct 2012 07:33:09 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.80,639,1344236400"; d="scan'208";a="239459086" Message-ID: <5087CF96.7010406@intel.com> Date: Wed, 24 Oct 2012 19:23:02 +0800 From: "Yan, Zheng" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:16.0) Gecko/20121016 Thunderbird/16.0.1 MIME-Version: 1.0 To: Stephane Eranian CC: LKML , Peter Zijlstra , "ak@linux.intel.com" Subject: Re: [PATCH V2 6/7] perf, x86: Use LBR call stack to get user callchain References: <1351058350-9159-1-git-send-email-zheng.z.yan@intel.com> <1351058350-9159-7-git-send-email-zheng.z.yan@intel.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5239 Lines: 115 On 10/24/2012 04:57 PM, Stephane Eranian wrote: > On Wed, Oct 24, 2012 at 7:59 AM, Yan, Zheng wrote: >> From: "Yan, Zheng" >> >> Try enabling the LBR call stack feature if event request recording >> callchain. Try utilizing the LBR call stack to get user callchain >> in case of there is no frame pointer. >> >> Signed-off-by: Yan, Zheng >> --- >> arch/x86/kernel/cpu/perf_event.c | 126 +++++++++++++++++++++-------- >> arch/x86/kernel/cpu/perf_event.h | 7 ++ >> arch/x86/kernel/cpu/perf_event_intel.c | 20 ++--- >> arch/x86/kernel/cpu/perf_event_intel_lbr.c | 3 + >> include/linux/perf_event.h | 6 ++ >> kernel/events/core.c | 11 ++- >> 6 files changed, 124 insertions(+), 49 deletions(-) >> >> diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c >> index 8ae8044..3bf2100 100644 >> --- a/arch/x86/kernel/cpu/perf_event.c >> +++ b/arch/x86/kernel/cpu/perf_event.c >> @@ -398,35 +398,46 @@ int x86_pmu_hw_config(struct perf_event *event) >> >> if (event->attr.precise_ip > precise) >> return -EOPNOTSUPP; >> - /* >> - * check that PEBS LBR correction does not conflict with >> - * whatever the user is asking with attr->branch_sample_type >> - */ >> - if (event->attr.precise_ip > 1 && x86_pmu.intel_cap.pebs_format < 2) { >> - u64 *br_type = &event->attr.branch_sample_type; >> - >> - if (has_branch_stack(event)) { >> - if (!precise_br_compat(event)) >> - return -EOPNOTSUPP; >> - >> - /* branch_sample_type is compatible */ >> - >> - } else { >> - /* >> - * user did not specify branch_sample_type >> - * >> - * For PEBS fixups, we capture all >> - * the branches at the priv level of the >> - * event. >> - */ >> - *br_type = PERF_SAMPLE_BRANCH_ANY; >> - >> - if (!event->attr.exclude_user) >> - *br_type |= PERF_SAMPLE_BRANCH_USER; >> - >> - if (!event->attr.exclude_kernel) >> - *br_type |= PERF_SAMPLE_BRANCH_KERNEL; >> - } >> + } >> + /* >> + * check that PEBS LBR correction does not conflict with >> + * whatever the user is asking with attr->branch_sample_type >> + */ >> + if (event->attr.precise_ip > 1 && x86_pmu.intel_cap.pebs_format < 2) { >> + u64 *br_type = &event->attr.branch_sample_type; >> + >> + if (has_branch_stack(event)) { >> + if (!precise_br_compat(event)) >> + return -EOPNOTSUPP; >> + >> + /* branch_sample_type is compatible */ >> + >> + } else { >> + /* >> + * user did not specify branch_sample_type >> + * >> + * For PEBS fixups, we capture all >> + * the branches at the priv level of the >> + * event. >> + */ >> + *br_type = PERF_SAMPLE_BRANCH_ANY; >> + >> + if (!event->attr.exclude_user) >> + *br_type |= PERF_SAMPLE_BRANCH_USER; >> + >> + if (!event->attr.exclude_kernel) >> + *br_type |= PERF_SAMPLE_BRANCH_KERNEL; >> + } >> + } else if (event->attr.sample_type & PERF_SAMPLE_CALLCHAIN) { >> + if (!has_branch_stack(event) && x86_pmu.attr_lbr_callstack) { >> + /* >> + * user did not specify branch_sample_type, >> + * try using the LBR call stack facility to >> + * record call chains in the user space. >> + */ >> + event->attr.branch_sample_type = >> + PERF_SAMPLE_BRANCH_USER | >> + PERF_SAMPLE_BRANCH_CALL_STACK; > > You are forcing user level here, but how do you know the user wanted > ONLY user level > callchains? > > The LBR call stack is used only when the frame pointer approach doesn't work. I think the kernel has frame pointer for the most cases. The second reason is that the LBR call stack only has 16 entries. I think it's too small to record both kernel and user call chains. Regards Yan, Zheng -- 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/