Messages in this thread | | | Date | Thu, 24 Oct 2019 15:41:33 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH V3 01/13] perf/core: Add new branch sample type for LBR TOS |
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On Tue, Oct 22, 2019 at 10:11:24AM -0700, kan.liang@linux.intel.com wrote: > From: Kan Liang <kan.liang@linux.intel.com> > > In LBR call stack mode, the depth of reconstructed LBR call stack limits > to the number of LBR registers. With LBR Top-of-Stack (TOS) information, > perf tool may stitch the stacks of two samples. The reconstructed LBR > call stack can break the HW limitation. > > Add a new branch sample type to retrieve LBR TOS. > > Only when the new branch sample type is set, the TOS information is > dumped into the PERF_SAMPLE_BRANCH_STACK output. > Perf tool should check the attr.branch_sample_type, and apply the > corresponding format for PERF_SAMPLE_BRANCH_STACK samples. > Otherwise, some user case may be broken. For example, users may parse a > perf.data, which include the new branch sample type, with an old version > perf tool (without the check). Users probably get incorrect information > without any warning. > > Signed-off-by: Kan Liang <kan.liang@linux.intel.com> > --- > include/linux/perf_event.h | 2 ++ > include/uapi/linux/perf_event.h | 10 +++++++++- > kernel/events/core.c | 11 +++++++++++ > 3 files changed, 22 insertions(+), 1 deletion(-) > > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h > index 61448c19a132..2b229ea1cc15 100644 > --- a/include/linux/perf_event.h > +++ b/include/linux/perf_event.h > @@ -92,6 +92,7 @@ struct perf_raw_record { > /* > * branch stack layout: > * nr: number of taken branches stored in entries[] > + * tos: Top-of-Stack (TOS) information. PMU specific data. > * > * Note that nr can vary from sample to sample > * branches (to, from) are stored from most recent > @@ -100,6 +101,7 @@ struct perf_raw_record { > */ > struct perf_branch_stack { > __u64 nr; > + __u64 tos; /* PMU specific data */ > struct perf_branch_entry entries[0]; > }; > > diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h > index bb7b271397a6..b1f022190571 100644 > --- a/include/uapi/linux/perf_event.h > +++ b/include/uapi/linux/perf_event.h > @@ -180,6 +180,8 @@ enum perf_branch_sample_type_shift { > > PERF_SAMPLE_BRANCH_TYPE_SAVE_SHIFT = 16, /* save branch type */ > > + PERF_SAMPLE_BRANCH_LBR_TOS_SHIFT = 17, /* save LBR TOS */
I think I prefer not having LBR here either, who knows what other hardware can make use of that.
On that, you've completely failed to Cc the other architecture that implement PERF_SAMPLE_BRANCH.
Aside from that I can live with this version.
> + > PERF_SAMPLE_BRANCH_MAX_SHIFT /* non-ABI */ > }; > > @@ -207,6 +209,8 @@ enum perf_branch_sample_type { > PERF_SAMPLE_BRANCH_TYPE_SAVE = > 1U << PERF_SAMPLE_BRANCH_TYPE_SAVE_SHIFT, > > + PERF_SAMPLE_BRANCH_LBR_TOS = 1U << PERF_SAMPLE_BRANCH_LBR_TOS_SHIFT, > + > PERF_SAMPLE_BRANCH_MAX = 1U << PERF_SAMPLE_BRANCH_MAX_SHIFT, > }; > > @@ -849,7 +853,11 @@ enum perf_event_type { > * char data[size];}&& PERF_SAMPLE_RAW > * > * { u64 nr; > - * { u64 from, to, flags } lbr[nr];} && PERF_SAMPLE_BRANCH_STACK > + * { u64 from, to, flags } lbr[nr]; > + * > + * # only available if PERF_SAMPLE_BRANCH_LBR_TOS is set > + * u64 tos; > + * } && PERF_SAMPLE_BRANCH_STACK > * > * { u64 abi; # enum perf_sample_regs_abi > * u64 regs[weight(mask)]; } && PERF_SAMPLE_REGS_USER > diff --git a/kernel/events/core.c b/kernel/events/core.c > index 9ec0b0bfddbd..18b0a7d2c67e 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -6343,6 +6343,11 @@ static void perf_output_read(struct perf_output_handle *handle, > perf_output_read_one(handle, event, enabled, running); > } > > +static inline bool perf_sample_save_lbr_tos(struct perf_event *event) > +{ > + return event->attr.branch_sample_type & PERF_SAMPLE_BRANCH_LBR_TOS; > +} > + > void perf_output_sample(struct perf_output_handle *handle, > struct perf_event_header *header, > struct perf_sample_data *data, > @@ -6432,6 +6437,8 @@ void perf_output_sample(struct perf_output_handle *handle, > > perf_output_put(handle, data->br_stack->nr); > perf_output_copy(handle, data->br_stack->entries, size); > + if (perf_sample_save_lbr_tos(event)) > + perf_output_put(handle, data->br_stack->tos); > } else { > /* > * we always store at least the value of nr > @@ -6619,7 +6626,11 @@ void perf_prepare_sample(struct perf_event_header *header, > if (data->br_stack) { > size += data->br_stack->nr > * sizeof(struct perf_branch_entry); > + > + if (perf_sample_save_lbr_tos(event)) > + size += sizeof(u64); > } > + > header->size += size; > } > > -- > 2.17.1 >
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