From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dennis Gnad Subject: Re: Understanding timestamps in perf.data Date: Thu, 3 Sep 2015 16:46:54 +0200 Message-ID: <55E85D5E.90400@kit.edu> References: <55E6C120.3030504@kit.edu> <55E6FCF9.60403@gmail.com> <55E71351.8010507@kit.edu> <55E72762.6030209@gmail.com> <55E7F47C.2000403@kit.edu> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from scc-mailout-kit-02.scc.kit.edu ([129.13.231.82]:40052 "EHLO scc-mailout-kit-02.scc.kit.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752004AbbICOrB (ORCPT ); Thu, 3 Sep 2015 10:47:01 -0400 In-Reply-To: Sender: linux-perf-users-owner@vger.kernel.org List-ID: To: Vince Weaver Cc: David Ahern , linux-perf-users@vger.kernel.org On 03.09.2015 14:52, Vince Weaver wrote > > The kernel itself has trouble going to 100Hz without causing a lot of > overhead and at 1kHz the NMI overhead gets high enough that the kernel > throttles things down. I haven't investigated why that is, it might be a > problem with how my tool is coded. For now I just gave up and am making > masurements at 10Hz. OK thanks for this information. I can probably now exclude the current perf-interface of the kernel. Maybe this is also interesting for you then: In the meantime I got some information for the x86 architecture. There, the performance counters can be read directly in userspace by the interface over MSR's similar to readmsr/msrtool, where a reliable interval of <10ms can be achieved. [1] For ARM, there seems to exist some specialized driver "gator" which I didn't take a closer look. Anyhow, I am currently looking at a Power7 system, and don't know of any other interfaces there than perf/oprofile. I will continue to try to find some more information about that. Best regards, Dennis [1] *F. Oboril*, J. Ewert, and M. B. Tahoori, "High-Resolution Online Power Monitoring for Modern Microprocessors," in Proceedings of Design, Automation & Test in Europe (*DATE*), 2015, France. Online available: *http://cdnc.itec.kit.edu/downloads/Papers/Oboril15DATE.pdf *