From mboxrd@z Thu Jan 1 00:00:00 1970 From: Milian Wolff Subject: Re: perf report --inline usability issues when sorting by function Date: Fri, 28 Apr 2017 00:03:34 +0200 Message-ID: <2212711.UdkHn3vGHL@agathebauer> References: <13103005.TJTgFMaJPi@agathebauer> Mime-Version: 1.0 Content-Type: multipart/signed; boundary="nextPart4461346.J12YbUo4Le"; micalg="sha1"; protocol="application/pkcs7-signature" Return-path: Received: from mail.kdab.com ([176.9.126.58]:56908 "EHLO mail.kdab.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1423257AbdD0WDi (ORCPT ); Thu, 27 Apr 2017 18:03:38 -0400 In-Reply-To: <13103005.TJTgFMaJPi@agathebauer> Sender: linux-perf-users-owner@vger.kernel.org List-ID: To: Milian Wolff Cc: Perf Users , "Jin, Yao" --nextPart4461346.J12YbUo4Le Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" On Donnerstag, 27. April 2017 23:09:10 CEST Milian Wolff wrote: > Hey Jin, others > > I observe a usability issue with the following example code: > > ~~~~~~~~~~~~~~~~~~~~ > #include > #include > #include > > using namespace std; > > int main() > { > uniform_real_distribution uniform(-1E5, 1E5); > default_random_engine engine; > double s = 0; > for (int i = 0; i < 10000000; ++i) { > s += uniform(engine); > } > cout << "random sum: " << s << '\n'; > return 0; > } > ~~~~~~~~~~~~~~~~~~~~ > > Compile it with `g++ -O2 -g` then record it with `perf record --call-graph > dwarf` and inspect the data with inliners enabled. Here are some excerpts > that show the issues: > > ~~~~~~~~~~~~~~~~~~~~ > $ perf report --stdio --inline --no-children > Failed to open [ext4], continuing without symbols > # To display the perf.data header info, please use --header/--header-only > options. > # > # > # Total Lost Samples: 0 > # > # Samples: 499 of event 'cycles' > # Event count (approx.): 329354953 > # > # Overhead Command Shared Object Symbol > # ........ ......... ................. ................................ > # > 96.70% ex_random ex_random [.] main > > ---main > __libc_start_main > _start > > 0.96% ex_random ld-2.25.so [.] do_lookup_x > > ---do_lookup_x > _dl_lookup_symbol_x > _dl_relocate_object > dl_main > _dl_sysdep_start > _dl_start > _dl_start_user > > 0.30% ex_random ld-2.25.so [.] _dl_lookup_symbol_x > ... > ~~~~~~~~~~~~~~~~~~~~~~ > > Note how no inlined frames are actually shown. I think the issue here is > that when we group by function name (the default), then multiple samples > with different IPs will get merged. Once we display the data then in e.g. > ui/stdio/ hist.c, we will only have one node left for this function, with > an arbitrary IP (of the first sample, I guess). > > This is problematic, because depending on the IP, different inlined call > stacks may have been used. This is observable for the above use-case by > changing the grouping algorithm, e.g.: > > ~~~~~~~~~~~~~~~~~~~~~~~ > $ perf report --stdio --inline --no-children -g srcline > Invalid callchain mode: srcline > Invalid callchain order: srcline > Failed to open [ext4], continuing without symbols > # To display the perf.data header info, please use --header/--header-only > options. > # > # > # Total Lost Samples: 0 > # > # Samples: 499 of event 'cycles' > # Event count (approx.): 329354953 > # > # Overhead Command Shared Object Symbol > # ........ ......... ................. ................................ > # > 96.70% ex_random ex_random [.] main > > |--28.97%--main random.tcc:3326 > | > | /usr/include/c++/6.3.1/bits/random.h:185 (inline) > | /usr/include/c++/6.3.1/bits/random.h:1818 (inline) > | /usr/include/c++/6.3.1/bits/random.h:1809 (inline) > | /home/milian/projects/kdab/training-material/addon/ > > profiling/build/ex_random/../../ex_random/main.cpp:13 (inline) > > | __libc_start_main > | _start > | > |--28.14%--main random.h:143 > | > | /usr/include/c++/6.3.1/bits/random.h:151 (inline) > | /usr/include/c++/6.3.1/bits/random.h:332 (inline) > | /usr/include/c++/6.3.1/bits/random.tcc:3332 (inline) > | /usr/include/c++/6.3.1/bits/random.h:185 (inline) > | /usr/include/c++/6.3.1/bits/random.h:1818 (inline) > | /usr/include/c++/6.3.1/bits/random.h:1809 (inline) > | /home/milian/projects/kdab/training-material/addon/ > > profiling/build/ex_random/../../ex_random/main.cpp:13 (inline) > > | __libc_start_main > | _start > > ... > ~~~~~~~~~~~~~~~~~~~~~~~ > > Has anyone any suggestion on how to fix this? Some ideas: > > - adapt the function aggregation to also take the inlined function into > account > - always add inlined frames to the graph > - keep all IPs and their cost even when aggregating functions I have no implemented the first option from the above list and sent a patch for review. Feedback welcome! It seems to work quite nicely in my tests. Thanks -- Milian Wolff | milian.wolff@kdab.com | Software Engineer KDAB (Deutschland) GmbH&Co KG, a KDAB Group company Tel: +49-30-521325470 KDAB - The Qt Experts --nextPart4461346.J12YbUo4Le Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQEHAQAAoIIUdzCCBGYw ggNOoAMCAQICEFEmCpMc4n+cw6VfeeByroIwDQYJKoZIhvcNAQEFBQAwgZMxCzAJBgNVBAYTAlVT MQswCQYDVQQIEwJVVDEXMBUGA1UEBxMOU2FsdCBMYWtlIENpdHkxHjAcBgNVBAoTFVRoZSBVU0VS VFJVU1QgTmV0d29yazEhMB8GA1UECxMYaHR0cDovL3d3dy51c2VydHJ1c3QuY29tMRswGQYDVQQD ExJVVE4gLSBEQVRBQ29ycCBTR0MwHhcNMDUwNjA3MDgwOTEwWhcNMTkwNjI0MTkwNjMwWjBvMQsw CQYDVQQGEwJTRTEUMBIGA1UEChMLQWRkVHJ1c3QgQUIxJjAkBgNVBAsTHUFkZFRydXN0IEV4dGVy bmFsIFRUUCBOZXR3b3JrMSIwIAYDVQQDExlBZGRUcnVzdCBFeHRlcm5hbCBDQSBSb290MIIBIjAN BgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAt/caM+byAAQtOeBOW+0fvGwPzbX6I7bO3psRM5ek 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