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Date: Wed, 13 Jun 2012 15:23:54 +0200 From: Jiri Olsa <jolsa@...hat.com> To: Stephane Eranian <eranian@...gle.com> Cc: acme@...hat.com, a.p.zijlstra@...llo.nl, mingo@...e.hu, paulus@...ba.org, cjashfor@...ux.vnet.ibm.com, fweisbec@...il.com, gorcunov@...nvz.org, tzanussi@...il.com, mhiramat@...hat.com, robert.richter@....com, fche@...hat.com, linux-kernel@...r.kernel.org, masami.hiramatsu.pt@...achi.com, drepper@...il.com, asharma@...com, benjamin.redelings@...cent.org Subject: Re: [PATCH 02/19] perf: Add ability to attach user level registers dump to sample On Wed, Jun 13, 2012 at 03:18:54PM +0200, Stephane Eranian wrote: > On Wed, Jun 13, 2012 at 3:12 PM, Jiri Olsa <jolsa@...hat.com> 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 <jolsa@...hat.com> 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 <fweisbec@...il.com> > >> > Signed-off-by: Jiri Olsa <jolsa@...hat.com> > >> > --- > >> > 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@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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