Messages in this thread | | | Subject | Re: [PATCH 1/2] tools/perf: Add reverse_fn to handle branch_stack endian issue | From | Madhavan Srinivasan <> | Date | Mon, 11 Oct 2021 19:59:41 +0530 |
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On 10/7/21 11:12 PM, Jiri Olsa wrote: > On Thu, Sep 30, 2021 at 12:34:09PM +0530, Madhavan Srinivasan wrote: >> branch_stack struct has bit field definition which >> produces different bit ordering for big/little endian. >> Because of this, when branch_stack sample is collected >> in a BE system and viewed/reported in a LE system, bit >> fields of the branch stack are not presented properly. >> To address this issue, a evsel__reverse64_branch_stack_flags() >> is defined and introduced in evsel__parse_sample. >> >> Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com> >> --- >> tools/perf/util/evsel.c | 64 +++++++++++++++++++++++++++++++++++++++-- >> tools/perf/util/evsel.h | 5 ++++ >> 2 files changed, 67 insertions(+), 2 deletions(-) >> >> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c >> index dbfeceb2546c..007be66b69a2 100644 >> --- a/tools/perf/util/evsel.c >> +++ b/tools/perf/util/evsel.c >> @@ -2221,6 +2221,46 @@ void __weak arch_perf_parse_sample_weight(struct perf_sample *data, >> data->weight = *array; >> } >> >> +u64 evsel__reverse64_branch_stack_flags(u64 value) >> +{ >> + u64 new_val = 0; >> + >> + /* >> + * branch_stack flag (u64) >> + * union { >> + * u64 values; >> + * struct { >> + * mispred:1 //target mispredicted >> + * predicted:1 //target predicted >> + * in_tx:1 //in transaction >> + * abort:1 //transaction abort >> + * cycles:16 //cycle count to last branch >> + * type:4 //branch type >> + * reserved:40 >> + * } >> + * } >> + */ > please describe in comment how the bitfield is swapped
Sure will do.
>> + if (bigendian()) { >> + new_val = reverse_64(value, 0, 1); >> + new_val |= reverse_64(value, 1, 1); >> + new_val |= reverse_64(value, 2, 1); >> + new_val |= reverse_64(value, 3, 1); >> + new_val |= reverse_64(value, 4, 16); >> + new_val |= reverse_64(value, 20, 4); >> + new_val |= reverse_64(value, 24, 40); >> + } else { >> + new_val = reverse_64(value, 63, 1); >> + new_val |= reverse_64(value, 62, 1); >> + new_val |= reverse_64(value, 61, 1); >> + new_val |= reverse_64(value, 60, 1); >> + new_val |= reverse_64(value, 44, 16); >> + new_val |= reverse_64(value, 40, 4); >> + new_val |= reverse_64(value, 0, 40); >> + } >> + >> + return new_val; >> +} >> + >> int evsel__parse_sample(struct evsel *evsel, union perf_event *event, >> struct perf_sample *data) >> { >> @@ -2408,6 +2448,8 @@ int evsel__parse_sample(struct evsel *evsel, union perf_event *event, >> if (type & PERF_SAMPLE_BRANCH_STACK) { >> const u64 max_branch_nr = UINT64_MAX / >> sizeof(struct branch_entry); >> + struct branch_entry *e; >> + unsigned int i; >> >> OVERFLOW_CHECK_u64(array); >> data->branch_stack = (struct branch_stack *)array++; >> @@ -2416,10 +2458,28 @@ int evsel__parse_sample(struct evsel *evsel, union perf_event *event, >> return -EFAULT; >> >> sz = data->branch_stack->nr * sizeof(struct branch_entry); >> - if (evsel__has_branch_hw_idx(evsel)) >> + if (evsel__has_branch_hw_idx(evsel)) { >> sz += sizeof(u64); >> - else >> + e = &data->branch_stack->entries[0]; >> + } else { >> data->no_hw_idx = true; >> + e = (struct branch_entry *)&data->branch_stack->hw_idx; > hum, why do we convert hw_idx? it's the same struct as entries? > please explain this in comment as well
No. IIUC, hw_idx is valid only if PERF_SAMPLE_BRANCH_HW_INDEX is applied. If not, then only nr and entries[] will be output-ed by kernel 42bbabed09ce ('perf tools: Add hw_idx in struct branch_stack')
> >> + } >> + >> + if (swapped) { >> + /* >> + * struct branch_flag does not have endian specific >> + * bit field definition. And bswap will not resolve the >> + * issue, since these are bit fields. >> + * >> + * evsel__reverse64_branch_stack_flags() uses a reverse64 >> + * macro to reverse the bit position based on the host >> + * endians. >> + */ >> + for (i = 0; i < data->branch_stack->nr; i++, e++) >> + e->flags.value = evsel__reverse64_branch_stack_flags(e->flags.value); >> + } >> + >> OVERFLOW_CHECK(array, sz, max_size); >> array = (void *)array + sz; >> } >> diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h >> index 1f7edfa8568a..1127c23710cf 100644 >> --- a/tools/perf/util/evsel.h >> +++ b/tools/perf/util/evsel.h >> @@ -482,4 +482,9 @@ struct evsel *evsel__leader(struct evsel *evsel); >> bool evsel__has_leader(struct evsel *evsel, struct evsel *leader); >> bool evsel__is_leader(struct evsel *evsel); >> void evsel__set_leader(struct evsel *evsel, struct evsel *leader); >> + >> +#define reverse_64(src, pos, size) \ >> + ((((src) >> (pos)) & ((1ull << (size)) - 1)) << (63 - ((pos) + (size) - 1))) > hum, is this reversing anything? > could you please add comment describing what this is doing?
Sure will do. Thanks for review Maddy
> thanks, jirka >> + >> +u64 evsel__reverse64_branch_stack_flags(u64 value); >> #endif /* __PERF_EVSEL_H */ >> -- >> 2.31.1 >>
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