Messages in this thread | | | Date | Fri, 11 Mar 2022 08:55:36 +0530 | Subject | Re: [PATCH V2 4/8] perf: Capture branch privilege information | From | Anshuman Khandual <> |
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On 3/10/22 15:51, James Clark wrote: > > > 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.
Makes sense.
> > 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.
Fair enough, will start the enum with PERF_BR_PRIV_UNKNOWN and expand the field 'perf_branch_entry.priv' to 3 bits instead, in order to accommodate any future needs regarding other captured privilege levels.
> > 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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