From patchwork Wed Sep 1 00:35:14 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Song Liu X-Patchwork-Id: 12468005 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-14.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 044BEC432BE for ; Wed, 1 Sep 2021 00:35:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D41E06103D for ; Wed, 1 Sep 2021 00:35:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240914AbhIAAgY (ORCPT ); Tue, 31 Aug 2021 20:36:24 -0400 Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:52266 "EHLO mx0b-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240844AbhIAAgX (ORCPT ); Tue, 31 Aug 2021 20:36:23 -0400 Received: from pps.filterd (m0109332.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.43/8.16.0.43) with SMTP id 1810Ufev025279 for ; Tue, 31 Aug 2021 17:35:27 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=from : to : cc : subject : date : message-id : content-type : content-transfer-encoding : mime-version; s=facebook; bh=xfJaQgEFutNFXHwxqE5t89p1I7MO4YmmYJYKZbVwTU4=; b=RoxxkhAlCK6II/ZzjpnpNSUOByRltX/hfQCzmnISFlMiYpzjU6gL4bKY7/ikRxeyAbAt Q7T0SN4OurkWX7GjjLsiVV6hwhPbXXz4iqXO/0zstpYZrCHFf8nYTKIsXIKzjy+o5sdC f2qvyPHkIWgPTMB4p0V47Yf+jh7LEAsBhh4= Received: from maileast.thefacebook.com ([163.114.130.16]) by mx0a-00082601.pphosted.com with ESMTP id 3asmx9dfe1-3 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Tue, 31 Aug 2021 17:35:27 -0700 Received: from intmgw001.05.ash7.facebook.com (2620:10d:c0a8:1b::d) by mail.thefacebook.com (2620:10d:c0a8:83::4) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.14; Tue, 31 Aug 2021 17:35:26 -0700 Received: by devbig006.ftw2.facebook.com (Postfix, from userid 4523) id 92286F58687E; Tue, 31 Aug 2021 17:35:20 -0700 (PDT) From: Song Liu To: , CC: , , , , , Song Liu Subject: [PATCH v4 bpf-next 0/3] bpf: introduce bpf_get_branch_snapshot Date: Tue, 31 Aug 2021 17:35:14 -0700 Message-ID: <20210901003517.3953145-1-songliubraving@fb.com> X-Mailer: git-send-email 2.30.2 X-FB-Internal: Safe X-FB-Source: Intern X-Proofpoint-ORIG-GUID: 6dVRIz7hVR8S6nJZnd9vro5aCaFM7D13 X-Proofpoint-GUID: 6dVRIz7hVR8S6nJZnd9vro5aCaFM7D13 X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.790 definitions=2021-08-31_10:2021-08-31,2021-08-31 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 adultscore=0 mlxlogscore=938 mlxscore=0 impostorscore=0 spamscore=0 lowpriorityscore=0 bulkscore=0 priorityscore=1501 phishscore=0 suspectscore=0 malwarescore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2107140000 definitions=main-2109010001 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net changes v3 => v4: 1. Do not reshuffle intel_pmu_disable_all(). Use some inline to save LBR entries. (Peter) 2. Move static_call(perf_snapshot_branch_stack) to the helper. (Alexei) 3. Add argument flags to bpf_get_branch_snapshot. (Andrii) 4. Make MAX_BRANCH_SNAPSHOT an enum (Andrii). And rename it as PERF_MAX_BRANCH_SNAPSHOT 5. Make bpf_get_branch_snapshot similar to bpf_read_branch_records. (Andrii) 6. Move the test target function to bpf_testmod. Updated kallsyms_find_next to work properly with modules. (Andrii) Changes v2 => v3: 1. Fix the use of static_call. (Peter) 2. Limit the use to perfmon version >= 2. (Peter) 3. Modify intel_pmu_snapshot_branch_stack() to use intel_pmu_disable_all and intel_pmu_enable_all(). Changes v1 => v2: 1. Rename the helper as bpf_get_branch_snapshot; 2. Fix/simplify the use of static_call; 3. Instead of percpu variables, let intel_pmu_snapshot_branch_stack output branch records to an output argument of type perf_branch_snapshot. Branch stack can be very useful in understanding software events. For example, when a long function, e.g. sys_perf_event_open, returns an errno, it is not obvious why the function failed. Branch stack could provide very helpful information in this type of scenarios. This set adds support to read branch stack with a new BPF helper bpf_get_branch_trace(). Currently, this is only supported in Intel systems. It is also possible to support the same feaure for PowerPC. The hardware that records the branch stace is not stopped automatically on software events. Therefore, it is necessary to stop it in software soon. Otherwise, the hardware buffers/registers will be flushed. One of the key design consideration in this set is to minimize the number of branch record entries between the event triggers and the hardware recorder is stopped. Based on this goal, current design is different from the discussions in original RFC [1]: 1) Static call is used when supported, to save function pointer dereference; 2) intel_pmu_lbr_disable_all is used instead of perf_pmu_disable(), because the latter uses about 10 entries before stopping LBR. With current code, on Intel CPU, LBR is stopped after 10 branch entries after fexit triggers: ID: 0 from intel_pmu_lbr_disable_all+58 to intel_pmu_lbr_disable_all+93 ID: 1 from intel_pmu_lbr_disable_all+54 to intel_pmu_lbr_disable_all+58 ID: 2 from intel_pmu_snapshot_branch_stack+88 to intel_pmu_lbr_disable_all+0 ID: 3 from bpf_get_branch_snapshot+77 to intel_pmu_snapshot_branch_stack+0 ID: 4 from __brk_limit+478052814 to bpf_get_branch_snapshot+0 ID: 5 from __brk_limit+478036039 to __brk_limit+478052760 ID: 6 from __bpf_prog_enter+34 to __brk_limit+478036027 ID: 7 from migrate_disable+60 to __bpf_prog_enter+9 ID: 8 from __bpf_prog_enter+4 to migrate_disable+0 ID: 9 from __brk_limit+478036022 to __bpf_prog_enter+0 ID: 10 from bpf_testmod_loop_test+22 to __brk_limit+478036003 ID: 11 from bpf_testmod_loop_test+20 to bpf_testmod_loop_test+13 ID: 12 from bpf_testmod_loop_test+20 to bpf_testmod_loop_test+13 ID: 13 from bpf_testmod_loop_test+20 to bpf_testmod_loop_test+13 ... [1] https://lore.kernel.org/bpf/20210818012937.2522409-1-songliubraving@fb.com/ Song Liu (3): perf: enable branch record for software events bpf: introduce helper bpf_get_branch_snapshot selftests/bpf: add test for bpf_get_branch_snapshot arch/x86/events/intel/core.c | 26 ++++- arch/x86/events/intel/ds.c | 8 -- arch/x86/events/perf_event.h | 10 +- include/linux/perf_event.h | 26 +++++ include/uapi/linux/bpf.h | 22 ++++ kernel/bpf/trampoline.c | 3 +- kernel/events/core.c | 2 + kernel/trace/bpf_trace.c | 40 +++++++ tools/include/uapi/linux/bpf.h | 22 ++++ .../selftests/bpf/bpf_testmod/bpf_testmod.c | 14 ++- .../bpf/prog_tests/get_branch_snapshot.c | 101 ++++++++++++++++++ .../selftests/bpf/progs/get_branch_snapshot.c | 44 ++++++++ tools/testing/selftests/bpf/trace_helpers.c | 37 +++++++ tools/testing/selftests/bpf/trace_helpers.h | 5 + 14 files changed, 345 insertions(+), 15 deletions(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c create mode 100644 tools/testing/selftests/bpf/progs/get_branch_snapshot.c --- 2.30.2