Messages in this thread | | | Date | Wed, 13 Jun 2012 15:12:40 +0200 | From | Jiri Olsa <> | Subject | Re: [PATCH 02/19] perf: Add ability to attach user level registers dump to sample |
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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@redhat.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@gmail.com> > > Signed-off-by: Jiri Olsa <jolsa@redhat.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..
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.
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