From mboxrd@z Thu Jan 1 00:00:00 1970 From: Milian Wolff Subject: Re: LBR unwinding for user defined dynamic trace point Date: Thu, 07 Apr 2016 17:05:07 +0200 Message-ID: <2173915.EElRzu5JW2@milian-kdab2> References: <2495974.rH49Pff4SO@milian-kdab2> <3862406.HVDrYIDCMl@milian-kdab2> <20150916185614.GF1747@two.firstfloor.org> Mime-Version: 1.0 Content-Type: multipart/signed; boundary="nextPart365014840.yeG5nFVFTP"; micalg="sha1"; protocol="application/pkcs7-signature" Return-path: Received: from mail.kdab.com ([176.9.126.58]:53505 "EHLO mail.kdab.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756447AbcDGPFS (ORCPT ); Thu, 7 Apr 2016 11:05:18 -0400 In-Reply-To: <20150916185614.GF1747@two.firstfloor.org> Sender: linux-perf-users-owner@vger.kernel.org List-ID: To: Andi Kleen Cc: 5A@linux.intel.com, linux-perf-users@vger.kernel.org --nextPart365014840.yeG5nFVFTP Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" On Wednesday, September 16, 2015 8:56:14 PM CEST Andi Kleen wrote: > On Wed, Sep 16, 2015 at 11:55:22AM +0200, Milian Wolff wrote: > > On Tuesday, September 15, 2015 7:02:37 AM CEST Andi Kleen wrote: > > > Milian Wolff writes: > > > > When I do the same with the Dwarf unwinder, it works just fine. Using > > > > the > > > > LBR unwinder with a performance counter like instructions also works > > > > fine. Does anyone know what the issue is here? > > > > > > LBR is only supported for PMU sampling at this point. > > > > OK, thanks. Can you give me some more information on why that is? Is it > > fundamentally not possible, or simply not yet implemented? > > For LBR callgraph it could be implemented. For some other LBR usages > there would be limitations, as there is no LBR freezing for software > trace points. Hey Andi, I read your articles on LBR on LWN, thanks a lot for that! I want to revive this older thread though: Could you tell me what would be required to get LBR callgraphs supported for trace points? I noticed that it also does not work with static tracepoints or software events: ~~~~~~~~~~~~~~~~~~~~~~~ $ perf record -e faults --call-graph lbr ls Error: The sys_perf_event_open() syscall returned with 95 (Operation not supported) for event (faults). /bin/dmesg may provide additional information. No CONFIG_PERF_EVENTS=y kernel support configured? $ perf record -e raw_syscalls:sys_enter --call-graph lbr ls Error: The sys_perf_event_open() syscall returned with 95 (Operation not supported) for event (raw_syscalls:sys_enter). /bin/dmesg may provide additional information. No CONFIG_PERF_EVENTS=y kernel support configured? ~~~~~~~~~~~~~~~~~~~~~~~ It does work fine for hardware events though: ~~~~~~~~~~~~~~~~~~~~~~~ $ perf record -e cache-misses --call-graph lbr ls WARNING: No sample_id_all support, falling back to unordered processing ... [ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 0.017 MB perf.data (6 samples) ] ~~~~~~~~~~~~~~~~~~~~~~~ Due to the reasons and advantages you point out in your article for LBR callgraphs, I'd love to see it supported for the above use-cases as well, if possible. If you can guide me, and it does not require me to patch the kernel itself, then I'm also willing to come up with a patch for perf. 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 --nextPart365014840.yeG5nFVFTP 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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