Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754001Ab2FMNYx (ORCPT ); Wed, 13 Jun 2012 09:24:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:4871 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753688Ab2FMNYw (ORCPT ); Wed, 13 Jun 2012 09:24:52 -0400 Date: Wed, 13 Jun 2012 15:23:54 +0200 From: Jiri Olsa To: Stephane Eranian Cc: acme@redhat.com, a.p.zijlstra@chello.nl, mingo@elte.hu, paulus@samba.org, cjashfor@linux.vnet.ibm.com, fweisbec@gmail.com, gorcunov@openvz.org, tzanussi@gmail.com, mhiramat@redhat.com, robert.richter@amd.com, fche@redhat.com, linux-kernel@vger.kernel.org, masami.hiramatsu.pt@hitachi.com, drepper@gmail.com, asharma@fb.com, benjamin.redelings@nescent.org Subject: Re: [PATCH 02/19] perf: Add ability to attach user level registers dump to sample Message-ID: <20120613132354.GC2538@m.brq.redhat.com> References: <1339420814-7379-1-git-send-email-jolsa@redhat.com> <1339420814-7379-3-git-send-email-jolsa@redhat.com> <20120613131240.GB2538@m.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3681 Lines: 77 On Wed, Jun 13, 2012 at 03:18:54PM +0200, Stephane Eranian wrote: > On Wed, Jun 13, 2012 at 3:12 PM, Jiri Olsa wrote: > > On Wed, Jun 13, 2012 at 01:16:44PM +0200, Stephane Eranian wrote: > >> On Mon, Jun 11, 2012 at 3:19 PM, Jiri Olsa wrote: > >> > Introducing sample_regs_user bitmask into perf_event_attr > >> > struct to define the user level registers we want to attach > >> > to the sample. The dump itself is triggered once the > >> > sample_regs_user is not empty. > >> > > >> > Only user level registers are dump at the moment. Meaning the > >> > register values of the user space context as it was before the > >> > user entered the kernel for whatever reason (syscall, irq, > >> > exception, or a PMI happening in userspace). > >> > > >> > The layout of the sample_regs_user bitmap is described in > >> > asm/perf_regs.h for archs that support register dump. > >> > > >> > This is going to be useful to bring Dwarf CFI based stack > >> > unwinding on top of samples. > >> > > >> > Signed-off-by: Frederic Weisbecker > >> > Signed-off-by: Jiri Olsa > >> > --- > >> > ?include/linux/perf_event.h | ? 10 ++++++- > >> > ?kernel/events/core.c ? ? ? | ? 61 ++++++++++++++++++++++++++++++++++++++++++++ > >> > ?2 files changed, 70 insertions(+), 1 deletions(-) > >> > > >> > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h > >> > index 1ce887a..d66cbeb 100644 > >> > --- a/include/linux/perf_event.h > >> > +++ b/include/linux/perf_event.h > >> > @@ -271,7 +271,13 @@ struct perf_event_attr { > >> > ? ? ? ? ? ? ? ?__u64 ? ? ? ? ? bp_len; > >> > ? ? ? ? ? ? ? ?__u64 ? ? ? ? ? config2; /* extension of config1 */ > >> > ? ? ? ?}; > >> > - ? ? ? __u64 ? branch_sample_type; /* enum branch_sample_type */ > >> > + ? ? ? __u64 ? branch_sample_type; /* enum perf_branch_sample_type */ > >> > + > >> > + ? ? ? /* > >> > + ? ? ? ?* Defines set of user regs to dump on samples. > >> > + ? ? ? ?* See asm/perf_regs.h for details. > >> > + ? ? ? ?*/ > >> > + ? ? ? __u64 ? sample_regs_user; > >> > ?}; > >> That's not enough. You also need to define PERF_SAMPLE_USER_REGS > >> for sample_type. Although the sample_regs_users might look like it's enough > >> to capture regs, there is a problem when it comes to parsing the record. You > >> need an ordering guarantee that is explicitly spelled out in the API (the header > >> file). In your current patch, I have no way of knowing that sample_regs_users > >> are saved after BRANCH_STACK (should you have that enabled). Remember > >> that you can turn on/off sampled infos at will in sample_type. Yet to find the > >> infos when parsing, you need to know the order. > > > > Well, the sample_regs_user != 0 substitute the PERF_SAMPLE_USER_REGS bit. > > The behaviour is the same as if there was that bit defined.. > > > No it's not the same. Looking at sample_regs_user != 0, do you know in which > order the regs array is going to appear RELATIVE to the other captured > information? > > Take sample_type = IP|CPU|PERIOD, sample_regs_users = EAX > > Now, I get the raw record, want to parse it. Which comes first the user_regs > or the IP, CPU, PERIOD? > > Worst, I add more entries to PERF_SAMPLE_*, are they laid out before or > after the regs? after.. but only because I know that.. yep, I think you're right, we should track it in the sample_type enum.. I'll add those 2 bits jirka -- 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/