Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754510Ab3J3OFT (ORCPT ); Wed, 30 Oct 2013 10:05:19 -0400 Received: from mail-qa0-f45.google.com ([209.85.216.45]:53840 "EHLO mail-qa0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752180Ab3J3OFS (ORCPT ); Wed, 30 Oct 2013 10:05:18 -0400 Date: Wed, 30 Oct 2013 10:13:11 -0400 (EDT) From: Vince Weaver To: Peter Zijlstra cc: Vince Weaver , Will Deacon , "linux-kernel@vger.kernel.org" , Ingo Molnar , Arnaldo Carvalho de Melo , eranian@google.com Subject: Re: perf: PERF_EVENT_IOC_PERIOD on ARM vs everywhere else In-Reply-To: <20131030095615.GG16117@laptop.programming.kicks-ass.net> Message-ID: References: <20131028085700.GB20218@mudshark.cambridge.arm.com> <20131029042810.GD22291@mudshark.cambridge.arm.com> <20131029134536.GD16117@laptop.programming.kicks-ass.net> <20131030095615.GG16117@laptop.programming.kicks-ass.net> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: MULTIPART/MIXED; BOUNDARY="8323329-945360069-1383142404=:8668" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2238 Lines: 54 This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. --8323329-945360069-1383142404=:8668 Content-Type: TEXT/PLAIN; charset=ISO-8859-7 Content-Transfer-Encoding: 8BIT On Wed, 30 Oct 2013, Peter Zijlstra wrote: > Right, it was one of those interfaces that people claimed were > absolutely required so I implemented them but then nobody actually tried > using them for a long while :-( Well, the initial perf_event code drop was a big huge new interface without much documentation and it took a while for people to come up to speed on it. People have tried to use PERF_EVENT_IOC_PERIOD but stopped because it was buggy. It is still used, as someone complaining to me about the manpage description not matching reality is what started this whole thread. There was a push for getting this issue fixed back in 2010 but it never went anywhere. The userspace users will report bugs, but they are usually intimidated by the linux-kernel list and won't push along changes themselves. Usually it's up to someone like me or Stephane to do that, and we miss things sometimes. The users will just find a workaround and drop the issue, especially if it's going to take years before the fix shows up in RHEL or whatever ancient vendor kernel they are using. > The below code should deal with both cases I think -- completely > untested. Uncompiled too I guess? kernel/events/core.c: In function ?perf_event_period?: kernel/events/core.c:3531: error: invalid type argument of ?->? (have ?local64_t?) make[3]: *** [kernel/events/core.o] Error 1 I also won't be able to test the ARM change, as my pandaboard won't boot with recent kernels (can't find the MMC root filesystem) and I haven't had time to track down why. Also even on a simple period changing test it often fails due to lost interrupts (the Cortex-A9 lost interrupt errata?). Vince --8323329-945360069-1383142404=:8668-- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/