From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753446Ab2FMNNK (ORCPT ); Wed, 13 Jun 2012 09:13:10 -0400 Received: from mx1.redhat.com ([209.132.183.28]:9490 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752262Ab2FMNNI (ORCPT ); Wed, 13 Jun 2012 09:13:08 -0400 Date: Wed, 13 Jun 2012 15:12:40 +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: <20120613131240.GB2538@m.brq.redhat.com> References: <1339420814-7379-1-git-send-email-jolsa@redhat.com> <1339420814-7379-3-git-send-email-jolsa@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 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.. After last discussion the idea was to keep this just with sample_regs_user != 0. I dont see any limitation except for being incosistent with the rest of the sample dumps. I'm all for having that PERF_SAMPLE_USER_REGS bit and the user stack bit as well. jirka