Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758243Ab2JXLrm (ORCPT ); Wed, 24 Oct 2012 07:47:42 -0400 Received: from mail-la0-f46.google.com ([209.85.215.46]:43006 "EHLO mail-la0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757491Ab2JXLrk (ORCPT ); Wed, 24 Oct 2012 07:47:40 -0400 MIME-Version: 1.0 In-Reply-To: <5087CF96.7010406@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> Date: Wed, 24 Oct 2012 13:47:38 +0200 Message-ID: Subject: Re: [PATCH V2 6/7] perf, x86: Use LBR call stack to get user callchain From: Stephane Eranian To: "Yan, Zheng" Cc: LKML , Peter Zijlstra , "ak@linux.intel.com" 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: 5537 Lines: 121 On Wed, Oct 24, 2012 at 1:23 PM, Yan, Zheng wrote: > 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. And where is that determination made? > 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. > It's even too small for many object oriented user programs as well. > 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/