From mboxrd@z Thu Jan 1 00:00:00 1970 From: Milian Wolff Subject: Re: [PATCH 0/7] generate full callchain cursor entries for inlined frames Date: Mon, 29 May 2017 20:36:25 +0200 Message-ID: <2384048.5gd4jAH0Hk@agathebauer> References: <20170518193411.22380-1-milian.wolff@kdab.com> <4449663.nJV0hUTq9C@milian-kdab2> <20170524150237.GA27760@danjae.aot.lge.com> Mime-Version: 1.0 Content-Type: multipart/signed; boundary="nextPart2768090.dWdSWA0L0Z"; micalg="sha1"; protocol="application/pkcs7-signature" Return-path: Received: from mail.kdab.com ([176.9.126.58]:50470 "EHLO mail.kdab.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750864AbdE2SgZ (ORCPT ); Mon, 29 May 2017 14:36:25 -0400 In-Reply-To: <20170524150237.GA27760@danjae.aot.lge.com> Sender: linux-perf-users-owner@vger.kernel.org List-ID: To: Namhyung Kim Cc: Linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, kernel-team@lge.com --nextPart2768090.dWdSWA0L0Z Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" On Mittwoch, 24. Mai 2017 17:02:37 CEST Namhyung Kim wrote: > On Wed, May 24, 2017 at 03:42:59PM +0200, Milian Wolff wrote: > > On Wednesday, May 24, 2017 1:46:04 PM CEST Milian Wolff wrote: > > > On Monday, May 22, 2017 11:06:43 AM CEST Namhyung Kim wrote: > > > > Why not making the fake symbol has start addr of the sample IP and > > > > length of 1. The histogram sort code also compares the sym->start > > > > which might confuse the output of the children mode too IMHO. > > > > > > I can try that out, thank you for the suggestion. But I think it can > > > easily > > > break in different ways. I.e. when the same inline function gets used at > > > different IPs, it should actually be considered to be the same function > > > when we group/merge/aggregate. I updated the `match_chain` function > > > accordingly, to do a symname / srcline comparison on inlined frames, > > > instead of relying on the symbol start/end. I think using the IP for > > > the fake symbols won't be more reliable here, don't you think? > > > > > > In the end, I think we'll always have to special-case inlined fake > > > symbols > > > when we aggregate data, since the sym start/end is always going to be > > > some > > > arbitrary value that may or may not be what we want it to be. Doing the > > > explicit comparison on e.g. srcline/symname is always going to be the > > > most > > > reliable option, as it also directly results in a proper aggregation > > > based > > > on the strings that the user will see in the end. > > > > I haven't yet tried it out, but I think I can come up with a way to break > > your approach easily. Assume the following pseudo-code: > > > > void tail() > > { > > > > instr1; // IP1 > > instr2; // IP2 > > > > } > > > > void mid() > > { > > > > tail(); > > > > } > > > > void main() > > { > > > > mid(); > > > > } > > > > Now, assume both `tail` and `mid` get inlined into `main`. If we get one > > sample each for both IP1 and IP2, we want the following merged structure > > if we merge based on symbol: > > > > sym | incl | self > > main | 2 | 0 > > mid | 2 | 0 > > tail | 2 | 2 > > > > If we would give the inlined fake-symbols a start of the IP, i.e. either > > IP1 or IP2, then we would end up with this (unexpected) behavior instead: > > > > sym | incl | self > > main | 2 | 0 > > mid | 1 | 0 > > mid | 1 | 0 > > tail | 1 | 1 > > tail | 1 | 1 > > > > The reason is that the fake symbols for the inlined frames would be > > considered to be different functions since their start/end are not equal. > > This is "wrong" in my eyes - we really have to do symbol name comparisons > > for inlined frames, and also include srcline if that is desired. > > That would depend on how we treat inlined function instances. Each > instance might be considered as same or not - but I think it'd be > better treating them as same for simplicity. > > Also currently perf aggregates samples using symbol name, but a new > sort key might be added to use symbol address later. Thus it'd be > better to be prepared for such change. > > > If you think the above is not a valid assessment, I'll try to change my > > patch series to use the IP + 1 trick you suggest. But I really don't > > think it's going to work. > > So I agree that we should do symbol name comparison, but I still > prefer setting fake symbol address to [IP, +1]. That would reduce > memory space for annotate as well. Can you expand on this? I can implement this, but without having a way to test I don't know whether I'm doing it right or not ;-) Note that fake symbols cannot be annotated from `perf report` currently. The browser just does nothing - no error, nothing. So I'm really unsure how this would influence the "memory space for annotate". 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 --nextPart2768090.dWdSWA0L0Z 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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