Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754193AbaBRGHr (ORCPT ); Tue, 18 Feb 2014 01:07:47 -0500 Received: from mga11.intel.com ([192.55.52.93]:48812 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754117AbaBRGHp (ORCPT ); Tue, 18 Feb 2014 01:07:45 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.97,500,1389772800"; d="scan'208";a="483239630" From: "Yan, Zheng" To: linux-kernel@vger.kernel.org Cc: a.p.zijlstra@chello.nl, mingo@kernel.org, acme@infradead.org, eranian@google.com, andi@firstfloor.org, "Yan, Zheng" Subject: [PATCH v3 00/14] perf, x86: Haswell LBR call stack support Date: Tue, 18 Feb 2014 14:07:27 +0800 Message-Id: <1392703661-15104-1-git-send-email-zheng.z.yan@intel.com> X-Mailer: git-send-email 1.8.5.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org For many profiling tasks we need the callgraph. For example we often need to see the caller of a lock or the caller of a memcpy or other library function to actually tune the program. Frame pointer unwinding is efficient and works well. But frame pointers are off by default on 64bit code (and on modern 32bit gccs), so there are many binaries around that do not use frame pointers. Profiling unchanged production code is very useful in practice. On some CPUs frame pointer also has a high cost. Dwarf2 unwinding also does not always work and is extremely slow (upto 20% overhead). Haswell has a new feature that utilizes the existing Last Branch Record facility to record call chains. When the feature is enabled, function call will be collected as normal, but as return instructions are executed the last captured branch record is popped from the on-chip LBR registers. The LBR call stack facility provides an alternative to get callgraph. It has some limitations too, but should work in most cases and is significantly faster than dwarf. Frame pointer unwinding is still the best default, but LBR call stack is a good alternative when nothing else works. This patch series adds LBR call stack support. User can enabled/disable this through an sysfs attribute file in the CPU PMU directory: echo 1 > /sys/bus/event_source/devices/cpu/lbr_callstack When profiling bc(1) on Fedora 19: echo 'scale=2000; 4*a(1)' > cmd; perf record -g fp bc -l < cmd If this feature is enabled, perf report output looks like: 50.36% bc bc [.] bc_divide | --- bc_divide execute run_code yyparse main __libc_start_main _start 33.66% bc bc [.] _one_mult | --- _one_mult bc_divide execute run_code yyparse main __libc_start_main _start 7.62% bc bc [.] _bc_do_add | --- _bc_do_add | |--99.89%-- 0x2000186a8 --0.11%-- [...] 6.83% bc bc [.] _bc_do_sub | --- _bc_do_sub | |--99.94%-- bc_add | execute | run_code | yyparse | main | __libc_start_main | _start --0.06%-- [...] 0.46% bc libc-2.17.so [.] __memset_sse2 | --- __memset_sse2 | |--54.13%-- bc_new_num | | | |--51.00%-- bc_divide | | execute | | run_code | | yyparse | | main | | __libc_start_main | | _start | | | |--30.46%-- _bc_do_sub | | bc_add | | execute | | run_code | | yyparse | | main | | __libc_start_main | | _start | | | --18.55%-- _bc_do_add | bc_add | execute | run_code | yyparse | main | __libc_start_main | _start | --45.87%-- bc_divide execute run_code yyparse main __libc_start_main _start If this feature is disabled, perf report output looks like: 50.49% bc bc [.] bc_divide | --- bc_divide 33.57% bc bc [.] _one_mult | --- _one_mult 7.61% bc bc [.] _bc_do_add | --- _bc_do_add 0x2000186a8 6.88% bc bc [.] _bc_do_sub | --- _bc_do_sub 0.42% bc libc-2.17.so [.] __memcpy_ssse3_back | --- __memcpy_ssse3_back The LBR call stack has following known limitations - Zero length calls are not filtered out by hardware - Exception handing such as setjmp/longjmp will have calls/returns not match - Pushing different return address onto the stack will have calls/returns not match - If callstack is deeper than the LBR, only the last entries are captured Changes since v1 - split change into more patches - introduce context switch callback and use it to flush LBR - use the context switch callback to save/restore LBR - dynamic allocate memory area for storing LBR stack, always switch the memory area during context switch - disable this feature by default - more description in change logs Changes since v2 - don't use xchg to switch PMU specific data - remove nr_branch_stack from struct perf_event_context - simplify the save/restore LBR stack logical - remove unnecessary 'has_branch_stack -> needs_branch_stack' conversion - more description in change logs -- 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/