Messages in this thread | | | Date | Thu, 10 Mar 2022 10:21:03 +0000 | Subject | Re: [PATCH V2 4/8] perf: Capture branch privilege information | From | James Clark <> |
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On 09/03/2022 03:36, Anshuman Khandual wrote: > Platforms like arm64 could capture privilege level information for all the > branch records. Hence this adds a new element in the struct branch_entry to > record the privilege level information, which could be requested through a > new event.attr.branch_sample_type based flag PERF_SAMPLE_BRANCH_PRIV_SAVE. > This flag helps user choose whether privilege information is captured. > > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Arnaldo Carvalho de Melo <acme@kernel.org> > Cc: Mark Rutland <mark.rutland@arm.com> > Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> > Cc: Jiri Olsa <jolsa@redhat.com> > Cc: Namhyung Kim <namhyung@kernel.org> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Will Deacon <will@kernel.org> > Cc: linux-arm-kernel@lists.infradead.org > Cc: linux-perf-users@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> > --- > include/uapi/linux/perf_event.h | 13 ++++++++++++- > 1 file changed, 12 insertions(+), 1 deletion(-) > > diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h > index d29280adc3c4..0e96e2017f68 100644 > --- a/include/uapi/linux/perf_event.h > +++ b/include/uapi/linux/perf_event.h > @@ -204,6 +204,8 @@ enum perf_branch_sample_type_shift { > > PERF_SAMPLE_BRANCH_HW_INDEX_SHIFT = 17, /* save low level index of raw branch records */ > > + PERF_SAMPLE_BRANCH_PRIV_SAVE_SHIFT = 18, /* save privillege mode */ > + > PERF_SAMPLE_BRANCH_MAX_SHIFT /* non-ABI */ > }; > > @@ -233,6 +235,8 @@ enum perf_branch_sample_type { > > PERF_SAMPLE_BRANCH_HW_INDEX = 1U << PERF_SAMPLE_BRANCH_HW_INDEX_SHIFT, > > + PERF_SAMPLE_BRANCH_PRIV_SAVE = 1U << PERF_SAMPLE_BRANCH_PRIV_SAVE_SHIFT, > + > PERF_SAMPLE_BRANCH_MAX = 1U << PERF_SAMPLE_BRANCH_MAX_SHIFT, > }; > > @@ -271,6 +275,12 @@ enum { > PERF_BR_NEW_MAX, > }; > > +enum { > + PERF_BR_USER = 0, > + PERF_BR_KERNEL = 1, > + PERF_BR_HV = 2, > +};
0 should be "PERF_BR_PRIV_UNKNOWN" so userspace knows if it was not enabled otherwise it will look like all samples are PERF_BR_USER when actually priv type recording was just disabled.
I think it's not even always possible to go backwards from a sample to work out what the event attributes were so this can be interpreted (taking all of perf script and every corner case into account).
Starting at 0=UNKNOWN is consistent with the other fields and makes parsing it a whole lot easier.
James
> + > #define PERF_SAMPLE_BRANCH_PLM_ALL \ > (PERF_SAMPLE_BRANCH_USER|\ > PERF_SAMPLE_BRANCH_KERNEL|\ > @@ -1386,7 +1396,8 @@ struct perf_branch_entry { > cycles:16, /* cycle count to last branch */ > type:4, /* branch type */ > new_type:4, /* additional branch type */ > - reserved:36; > + priv:2, /* privilege level */ > + reserved:34; > }; > > union perf_sample_weight {
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