From mboxrd@z Thu Jan 1 00:00:00 1970 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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 5609CCA9EA0 for ; Tue, 22 Oct 2019 05:45:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2329121783 for ; Tue, 22 Oct 2019 05:45:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731052AbfJVFow (ORCPT ); Tue, 22 Oct 2019 01:44:52 -0400 Received: from mga17.intel.com ([192.55.52.151]:54004 "EHLO mga17.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725788AbfJVFov (ORCPT ); Tue, 22 Oct 2019 01:44:51 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga107.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 21 Oct 2019 22:44:51 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.67,326,1566889200"; d="scan'208";a="372408710" Received: from linux.intel.com ([10.54.29.200]) by orsmga005.jf.intel.com with ESMTP; 21 Oct 2019 22:44:50 -0700 Received: from [10.249.230.171] (abudanko-mobl.ccr.corp.intel.com [10.249.230.171]) by linux.intel.com (Postfix) with ESMTP id 53FA958029D; Mon, 21 Oct 2019 22:44:47 -0700 (PDT) From: Alexey Budankov Subject: [PATCH v4 0/4]: perf/core: fix restoring of Intel LBR call stack on a context switch To: Peter Zijlstra Cc: Arnaldo Carvalho de Melo , Ingo Molnar , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Andi Kleen , Kan Liang , Stephane Eranian , Ian Rogers , Song Liu , linux-kernel Organization: Intel Corp. Message-ID: Date: Tue, 22 Oct 2019 08:44:46 +0300 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Restore Intel LBR call stack from cloned inactive task perf context on a context switch. This change inherently addresses inconsistency in LBR call stack data provided on a sample in record profiling mode: $ perf record -N -B -T -R --call-graph lbr \ -e cpu/period=0xcdfe60,event=0x3c,name=\'CPU_CLK_UNHALTED.THREAD\'/Duk \ --clockid=monotonic_raw -- ./miniFE.x nx 25 ny 25 nz 25 Let's assume threads A, B, C belonging to the same process. B and C are siblings of A and their perf contexts are treated as equivalent. At some point B blocks on a futex (non preempt context switch). B's LBRs are preserved at B's perf context task_ctx_data and B's events are removed from PMU and disabled. B's perf context becomes inactive. Later C gets on a cpu, runs, gets profiled and eventually switches to the awaken but not yet running B. The optimized context switch path is executed swapping B's and C's task_ctx_data pointers at perf event contexts. So C's task_ctx_data will refer preserved B's LBRs on the following switch-in event. However, as far B's perf context is inactive there is no enabled events in there and B's task_ctx_data->lbr_callstack_users is equal to 0. When B gets on the cpu B's events reviving is skipped following the optimized context switch path and B's task_ctx_data->lbr_callstack_users remains 0. Thus B's LBR's are not restored by pmu sched_task() code called in the end of perf context switch-in callback for B. In the report that manifests as having short fragments of B's call stack, still tracked by LBR's HW between adjacent samples, but the whole thread call tree doesn't aggregate. The fix has been evaluated when profiling miniFE [1] (C++, OpenMP) workload running 64 threads on Intel Skylake EP(64 core, 2 sockets): $ perf report --call-graph callee,flat 5.3.0-rc6+ (tip perf/core) - fixed - 92.66% 82.64% miniFE.x libiomp5.so [.] _INTERNAL_25_______src_kmp_barrier_cpp_1d20fae8::__kmp_hyper_barrier_release - 69.14% _INTERNAL_25_______src_kmp_barrier_cpp_1d20fae8::__kmp_hyper_barrier_release __kmp_fork_barrier __kmp_launch_thread _INTERNAL_24_______src_z_Linux_util_c_3e0095e6::__kmp_launch_worker start_thread __clone - 21.89% _INTERNAL_25_______src_kmp_barrier_cpp_1d20fae8::__kmp_hyper_barrier_release __kmp_barrier __kmpc_reduce_nowait miniFE::cg_solve, miniFE::Vector, miniFE::matvec_std, miniFE::Vector, miniFE::Vector, miniFE::matvec_std, miniFE::Vector, miniFE::Vector, miniFE::matvec_std, miniFE::Vector, miniFE::Vector, miniFE::matvec_std, miniFE::Vector