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Thu, 21 Oct 2021 06:25:17 -0700 (PDT) X-Google-Smtp-Source: ABdhPJyFjOV/ylQQMALuxiAyz0iJ8blr1z08y94yE9g1hAByMOvPKYeKua3Qlc6daZzoBrkgVqAk+w== X-Received: by 2002:a50:c355:: with SMTP id q21mr2064244edb.161.1634822717435; Thu, 21 Oct 2021 06:25:17 -0700 (PDT) Received: from krava ([83.240.63.48]) by smtp.gmail.com with ESMTPSA id y6sm2588772ejf.58.2021.10.21.06.25.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 21 Oct 2021 06:25:17 -0700 (PDT) Date: Thu, 21 Oct 2021 15:25:15 +0200 From: Jiri Olsa To: Madhavan Srinivasan Cc: acme@kernel.org, michael@ellerman.id.au, eranian@google.com, mark.rutland@arm.com, namhyung@kernel.org, kjain@linux.ibm.com, atrajeev@linux.vnet.ibm.com, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/2] tools/perf: Add bitfield_swap to handle branch_stack endian issue Message-ID: References: <20211016125059.691856-1-maddy@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211016125059.691856-1-maddy@linux.ibm.com> Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org On Sat, Oct 16, 2021 at 06:20:58PM +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__bitfield_swap_branch_stack() > is defined and introduced in evsel__parse_sample. > > Signed-off-by: Madhavan Srinivasan > --- > Changelog v1: > - Renamed function and macro > - Added comments in code > > tools/perf/util/evsel.c | 74 +++++++++++++++++++++++++++++++++++++++-- > tools/perf/util/evsel.h | 13 ++++++++ > 2 files changed, 85 insertions(+), 2 deletions(-) > > diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c > index dbfeceb2546c..746e642d4d32 100644 > --- a/tools/perf/util/evsel.c > +++ b/tools/perf/util/evsel.c > @@ -2221,6 +2221,51 @@ void __weak arch_perf_parse_sample_weight(struct perf_sample *data, > data->weight = *array; > } > > +u64 evsel__bitfield_swap_branch_flags(u64 value) > +{ > + u64 new_val = 0; > + > + /* > + * branch_flags > + * 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 > + * } > + * } > + * > + * Avoid bswap64() the entire branch_flag.value, > + * as it has variable bit-field sizes. Instead the > + * macro takes the bit-field position/size, > + * swaps it based on the host endianness. > + */ > + if (bigendian()) { > + new_val = bitfield_swap(value, 0, 1); > + new_val |= bitfield_swap(value, 1, 1); > + new_val |= bitfield_swap(value, 2, 1); > + new_val |= bitfield_swap(value, 3, 1); > + new_val |= bitfield_swap(value, 4, 16); > + new_val |= bitfield_swap(value, 20, 4); > + new_val |= bitfield_swap(value, 24, 40); > + } else { > + new_val = bitfield_swap(value, 63, 1); > + new_val |= bitfield_swap(value, 62, 1); > + new_val |= bitfield_swap(value, 61, 1); > + new_val |= bitfield_swap(value, 60, 1); > + new_val |= bitfield_swap(value, 44, 16); > + new_val |= bitfield_swap(value, 40, 4); > + new_val |= bitfield_swap(value, 0, 40); > + } > + > + return new_val; > +} > + > int evsel__parse_sample(struct evsel *evsel, union perf_event *event, > struct perf_sample *data) > { > @@ -2408,6 +2453,8 @@ 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 +2463,33 @@ 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; > + /* > + * if the PERF_SAMPLE_BRANCH_HW_INDEX is not applied, > + * only nr and entries[] will be output by kernel. > + */ > + e = (struct branch_entry *)&data->branch_stack->hw_idx; > + } > + > + if (swapped) { thanks for all the comments, make it easy to review > + /* > + * struct branch_flag does not have endian > + * specific bit field definition. And bswap > + * will not resolve the issue, since these > + * are bit fields. > + * > + * evsel__bitfield_swap_branch_flags() uses a > + * bitfield_swap macro to swap the bit position > + * based on the host endians. > + */ > + for (i = 0; i < data->branch_stack->nr; i++, e++) > + e->flags.value = evsel__bitfield_swap_branch_flags(e->flags.value); one last thing that confuses me.. the sample is already swapped at this point, right? with perf_event__all64_swap function should you swap it back first and then do the proper bitfield swap? like we do in PERF_SAMPLE_RAW to get proper u32 values thanks, jirka > + } > + > 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..2e82cdbe2c08 100644 > --- a/tools/perf/util/evsel.h > +++ b/tools/perf/util/evsel.h > @@ -482,4 +482,17 @@ 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); > + > +/* > + * Macro to swap the bit-field postition and size. > + * Used when, > + * - dont need to swap the entire u64 && > + * - when u64 has variable bit-field sizes && > + * - when presented in a host endian which is different > + * than the source endian of the perf.data file > + */ > +#define bitfield_swap(src, pos, size) \ > + ((((src) >> (pos)) & ((1ull << (size)) - 1)) << (63 - ((pos) + (size) - 1))) > + > +u64 evsel__bitfield_swap_branch_flags(u64 value); > #endif /* __PERF_EVSEL_H */ > -- > 2.31.1 >