From mboxrd@z Thu Jan 1 00:00:00 1970 From: Milian Wolff via lttng-dev Subject: Re: LTTng user-space callstacks Date: Fri, 27 Mar 2020 18:18:09 +0100 Message-ID: <2063300.72vocr9iq0@agathebauer> References: <570185028.14544.1585317308324.JavaMail.zimbra@efficios.com> Reply-To: Milian Wolff Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============7286066116789692099==" Return-path: Received: from mail.kdab.com (mail.kdab.com [176.9.126.58]) by lists.lttng.org (Postfix) with ESMTPS id 48ppTm2gftz1WPB for ; Fri, 27 Mar 2020 13:18:20 -0400 (EDT) In-Reply-To: <570185028.14544.1585317308324.JavaMail.zimbra@efficios.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: lttng-dev-bounces@lists.lttng.org Sender: "lttng-dev" To: Valentin Grigorev , Mathieu Desnoyers Cc: lttng-dev List-Id: lttng-dev@lists.lttng.org --===============7286066116789692099== Content-Type: multipart/signed; boundary="nextPart2440722.7s5MMGUR32"; micalg="sha256"; protocol="application/pkcs7-signature" --nextPart2440722.7s5MMGUR32 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="iso-8859-1" On Freitag, 27. M=E4rz 2020 14:55:08 CET Mathieu Desnoyers wrote: > Last time I checked, the main issue with perf's handling of cases that la= ck > frame pointers is that they grab a ~2-4kB worth of stack data into the > trace, and then post-process it with libunwind. This might be OK for > sampling use-cases, but is not something I consider appropriate for traci= ng > due to considerably increased use of tracing throughput. >=20 > Has the situation changed on the perf side ? Perf still does this. But heaptrack, of which I'm the main author, uses=20 libunwind to unwind on every heap allocation and it's plenty fast. Obviousl= y=20 the impact is measureable and it's far away from even close to zero overhea= d.=20 But it's super useful. I guess having that capability in LTTng would be=20 similarly useful and if it's documented to have an overhead people can use = it=20 with care. Cheers =2D-=20 Milian Wolff | milian.wolff@kdab.com | Senior Software Engineer KDAB (Deutschland) GmbH, a KDAB Group company Tel: +49-30-521325470 KDAB - The Qt, C++ and OpenGL Experts --nextPart2440722.7s5MMGUR32 Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCDEIw ggXmMIIDzqADAgECAhBqm+E4O/8ra58B1dm4p1JWMA0GCSqGSIb3DQEBDAUAMIGFMQswCQYDVQQG EwJHQjEbMBkGA1UECBMSR3JlYXRlciBNYW5jaGVzdGVyMRAwDgYDVQQHEwdTYWxmb3JkMRowGAYD VQQKExFDT01PRE8gQ0EgTGltaXRlZDErMCkGA1UEAxMiQ09NT0RPIFJTQSBDZXJ0aWZpY2F0aW9u IEF1dGhvcml0eTAeFw0xMzAxMTAwMDAwMDBaFw0yODAxMDkyMzU5NTlaMIGXMQswCQYDVQQGEwJH QjEbMBkGA1UECBMSR3JlYXRlciBNYW5jaGVzdGVyMRAwDgYDVQQHEwdTYWxmb3JkMRowGAYDVQQK ExFDT01PRE8gQ0EgTGltaXRlZDE9MDsGA1UEAxM0Q09NT0RPIFJTQSBDbGllbnQgQXV0aGVudGlj YXRpb24gYW5kIFNlY3VyZSBFbWFpbCBDQTCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEB 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