Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753064Ab3F2AJ7 (ORCPT ); Fri, 28 Jun 2013 20:09:59 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:60018 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752720Ab3F2AJ6 (ORCPT ); Fri, 28 Jun 2013 20:09:58 -0400 Date: Fri, 28 Jun 2013 17:09:51 -0700 From: Sukadev Bhattiprolu To: Will Deacon Cc: Jed Davis , Peter Zijlstra , Paul Mackerras , Ingo Molnar , Arnaldo Carvalho de Melo , Russell King , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] perf: ARM: Record the user-mode PC in the call chain. Message-ID: <20130629000951.GA5117@us.ibm.com> References: <20130613232111.GA12536@mozilla.com> <20130618131319.GC6801@mudshark.cambridge.arm.com> <20130620031706.GB27428@mozilla.com> <20130620090728.GA2842@mudshark.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130620090728.GA2842@mudshark.cambridge.arm.com> X-Operating-System: Linux 2.0.32 on an i486 User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13062900-7182-0000-0000-000007938690 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3250 Lines: 84 Will Deacon [will.deacon@arm.com] wrote: | On Thu, Jun 20, 2013 at 04:17:06AM +0100, Jed Davis wrote: | > On Tue, Jun 18, 2013 at 02:13:19PM +0100, Will Deacon wrote: | > > On Fri, Jun 14, 2013 at 12:21:11AM +0100, Jed Davis wrote: | > > > With this change, we no longer lose the innermost entry in the user-mode | > > > part of the call chain. See also the x86 port, which includes the ip. | > > > | > > > It's possible to partially work around this problem by post-processing | > > > the data to use the PERF_SAMPLE_IP value, but this works only if the CPU | > > > wasn't in the kernel when the sample was taken. | > > | > > Thanks. I guess we need something similar for arm64 too. Could you cook a | > > similar patch please? | > | > Done (and tested, on the ARM V8 Foundation Model). | | Wow, I didn't expect you to test it. Thanks! | | > It looked as if the powerpc and sparc ports might have similar issues, | > but I haven't checked on them yet. | | I can extract some hardware from the pile in the corner of my flat if you | want a hand with testing. Interesting. Powerpc already saves the next_ip for the first entry: arch/powerpc/perf/callchain.c: perf_callchain_user_64(): ... next_ip = perf_instruction_pointer(regs); lr = regs->link; sp = regs->gpr[1]; perf_callchain_store(entry, next_ip); for (;;) { Do you have a test case/output that I can run on Power ? We actually have the opposite problem where we see duplication in callchains like this. We considered not saving the "link register" but that seems to break for a "leaf-node" functions. 13.65% sprintft libc-2.12.so [.] __random | --- __random | |--62.82%-- __random | | | |--97.31%-- rand | | do_my_sprintf | | main | | generic_start_main | | __libc_start_main | | 0x0 | | | --2.69%-- do_my_sprintf | main | generic_start_main | __libc_start_main | 0x0 | --37.18%-- rand | |--93.30%-- rand | do_my_sprintf | main | generic_start_main | __libc_start_main | 0x0 | --6.70%-- do_my_sprintf main generic_start_main __libc_start_main 0x0 -- 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/