From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933616AbdKBSQD (ORCPT ); Thu, 2 Nov 2017 14:16:03 -0400 Received: from mail-pg0-f66.google.com ([74.125.83.66]:47412 "EHLO mail-pg0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932438AbdKBSQC (ORCPT ); Thu, 2 Nov 2017 14:16:02 -0400 X-Google-Smtp-Source: ABhQp+Q8afWofV0MrfqYeTlOUBz2bI5ZUzGTe2oCurwtrfnAUPAsv+EIFsXFBjZEJbKM7jXRXL6KLA== From: Stephane Eranian To: linux-kernel@vger.kernel.org Cc: acme@redhat.com, peterz@infradead.org, mingo@elte.hu, ak@linux.intel.com, kan.liang@intel.com, jolsa@redhat.com Subject: [PATCH v2 0/5] perf: add support for capturing skid IP Date: Thu, 2 Nov 2017 11:15:54 -0700 Message-Id: <1509646559-919-1-git-send-email-eranian@google.com> X-Mailer: git-send-email 2.7.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This patchs adds a new sample record type called PERF_SAMPLE_SKID_IP. The goal is to record the unmodified interrupted instruction pointer (IP) as seen by the kernel and reflected in the machine state. On some architectures, it is possible to avoid the IP skid using hardware support. For instance, on Intel x86, the use of PEBS helps eliminate the skid on Haswell and later processors. On older Intel processor, software, i.e., the kernel, may succeed in eliminating the skid. Without this patch, on Haswell processors, if you set: - attr.precise = 0, then you get the skid IP - attr.precise = 1, then you get the skid PEBS ip (off-by-1) - attr.precise = 2, then you get the skidless PEBS ip The IP is captured when the event has PERF_SAMPLE_IP set in sample_type. However, there are certain measurements where you need to have BOTH the skidless IP and the skid IP. For instance, when studying branches, the skid IP usually points to the target of the branch while the skidless IP points to the branch instruction itself. Today, it is not possible to retrieve both at the same time. This patch makes this possible by specifying PERF_SAMPLE_IP|PERF_SAMPLE_SKID_IP. As an example, consider the following code snipet: 37.51 42c2ed je 42c2f3 42c2ef add $0x1,%rdx 42c2f3 sub $0x1,%rax When using PEBS (precise=2) and sampling on BR_INST_RETIRED.CONDITIONAL, the IP always points to 0x42c2ed. With precise=1, the IP would point to 0x42c2f3. It is interesting to collect both IPs in a single run to determine how often the conditional branch is taken vs. non-taken. Understanding the skid is also interesting for other precise events. In V2, we rebased to 10d94ff4d558 (v4.14-rc7). Stephane Eranian (5): perf/core: add PERF_RECORD_SAMPLE_SKID_IP record type perf/x86: add PERF_SAMPLE_SKID_IP support for X86 PEBS perf/tools: add support for PERF_SAMPLE_SKID_IP perf/record: add support for sampling skid ip perf/script: add support for skid ip arch/x86/events/intel/ds.c | 7 +++++++ include/linux/perf_event.h | 2 ++ include/uapi/linux/perf_event.h | 4 +++- kernel/events/core.c | 14 ++++++++++++++ tools/include/uapi/linux/perf_event.h | 4 +++- tools/perf/Documentation/perf-record.txt | 8 ++++++++ tools/perf/builtin-record.c | 2 ++ tools/perf/builtin-script.c | 6 ++++++ tools/perf/perf.h | 1 + tools/perf/util/event.h | 1 + tools/perf/util/evsel.c | 10 ++++++++++ tools/perf/util/session.c | 3 +++ 12 files changed, 60 insertions(+), 2 deletions(-) -- 2.7.4