Messages in this thread | | | From | Stephane Eranian <> | Date | Thu, 16 Sep 2021 23:48:31 -0700 | Subject | Re: [PATCH v1 01/13] perf/core: add union to struct perf_branch_entry |
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Hi,
Thanks for fixing this in the perf tool. But what about the struct branch_entry in the header?
On Thu, Sep 16, 2021 at 11:38 PM Madhavan Srinivasan <maddy@linux.ibm.com> wrote: > > > On 9/15/21 11:33 AM, Stephane Eranian wrote: > > Michael, > > > > > > On Fri, Sep 10, 2021 at 7:16 AM Michael Ellerman <mpe@ellerman.id.au> wrote: > >> Michael Ellerman <mpe@ellerman.id.au> writes: > >>> Peter Zijlstra <peterz@infradead.org> writes: > >>>> On Thu, Sep 09, 2021 at 12:56:48AM -0700, Stephane Eranian wrote: > >>>>> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h > >>>>> index f92880a15645..eb11f383f4be 100644 > >>>>> --- a/include/uapi/linux/perf_event.h > >>>>> +++ b/include/uapi/linux/perf_event.h > >>>>> @@ -1329,13 +1329,18 @@ union perf_mem_data_src { > >>>>> struct perf_branch_entry { > >>>>> __u64 from; > >>>>> __u64 to; > >>>>> - __u64 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; > >>>>> + union { > >>>>> + __u64 val; /* to make it easier to clear all fields */ > >>>>> + struct { > >>>>> + __u64 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; > >>>>> + }; > >>>>> + }; > >>>>> }; > >>>> > >>>> Hurpmh... all other bitfields have ENDIAN_BITFIELD things except this > >>>> one. Power folks, could you please have a look? > >>> The bit number of each field changes between big and little endian, but > >>> as long as kernel and userspace are the same endian, and both only > >>> access values via the bitfields then it works. > >> ... > >>> It does look like we have a bug in perf tool though, if I take a > >>> perf.data from a big endian system to a little endian one I don't see > >>> any of the branch flags decoded. eg: > >>> > >>> BE: > >>> > >>> 2413132652524 0x1db8 [0x2d0]: PERF_RECORD_SAMPLE(IP, 0x1): 5279/5279: 0xc00000000045c028 period: 923003 addr: 0 > >>> ... branch stack: nr:28 > >>> ..... 0: c00000000045c028 -> c00000000dce7604 0 cycles P 0 > >>> > >>> LE: > >>> > >>> 2413132652524 0x1db8 [0x2d0]: PERF_RECORD_SAMPLE(IP, 0x1): 5279/5279: 0xc00000000045c028 period: 923003 addr: 0 > >>> ... branch stack: nr:28 > >>> ..... 0: c00000000045c028 -> c00000000dce7604 0 cycles 0 > >>> ^ > >>> missing P > >>> > >>> I guess we're missing a byte swap somewhere. > >> Ugh. We _do_ have a byte swap, but we also need a bit swap. > >> > >> That works for the single bit fields, not sure if it will for the > >> multi-bit fields. > >> > >> So that's a bit of a mess :/ > >> > > Based on what I see in perf_event.h for other structures, I think I > > can make up what you would need for struct branch_entry. But Iit would > > be easier if you could send me a patch that you would have verified on > > your systems. > > Thanks. > Attached patch fixes the issue. Have tested both in both in BE and LE case. > > Maddy > > From f816ba2e6ef8d5975f78442d7ecb50d66c3c4326 Mon Sep 17 00:00:00 2001 > From: Madhavan Srinivasan <maddy@linux.ibm.com> > Date: Wed, 15 Sep 2021 22:29:09 +0530 > Subject: [RFC PATCH] tools/perf: Add reverse_64b macro > > branch_stack struct has bit field definition > producing different bit ordering for big/little endian. > Because of this, when branch_stack sample collected > in a BE system viewed/reported in a LE system, > bit fields of the branch stack are not presented > properly. To address this issue, a reverse_64b > macro is defined and introduced in evsel__parse_sample. > > Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com> > --- > tools/perf/util/evsel.c | 35 +++++++++++++++++++++++++++++++++-- > 1 file changed, 33 insertions(+), 2 deletions(-) > > diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c > index dbfeceb2546c..3151606e516e 100644 > --- a/tools/perf/util/evsel.c > +++ b/tools/perf/util/evsel.c > @@ -2221,6 +2221,9 @@ void __weak arch_perf_parse_sample_weight(struct > perf_sample *data, > data->weight = *array; > } > > +#define reverse_64b(src, pos, size) \ > + (((src >> pos) & (( 1ull <<size) - 1)) << (63 - (pos + size - 1))) > + > int evsel__parse_sample(struct evsel *evsel, union perf_event *event, > struct perf_sample *data) > { > @@ -2408,6 +2411,8 @@ 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 i; > > OVERFLOW_CHECK_u64(array); > data->branch_stack = (struct branch_stack *)array++; > @@ -2416,10 +2421,36 @@ 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; > + } > + > + if (swapped) { > + for (i = 0; i < data->branch_stack->nr; i++, e++) { > + u64 new_val = 0; > + > + /* mispred:1 target mispredicted */ > + new_val = reverse_64b(e->flags.value, 0, 1); > + /* predicted:1 target predicted */ > + new_val |= reverse_64b(e->flags.value, 1, 1); > + /* in_tx:1 in transaction */ > + new_val |= reverse_64b(e->flags.value, 2, 1); > + /* abort:1 transaction abort */ > + new_val |= reverse_64b(e->flags.value, 3, 1); > + /* cycles:16 cycle count to last branch */ > + new_val |= reverse_64b(e->flags.value, 4, 16); > + /* type:4 branch type */ > + new_val |= reverse_64b(e->flags.value, 20, 4); > + /* reserved:40 */ > + new_val |= reverse_64b(e->flags.value, 24, 40); > + e->flags.value = new_val; > + } > + } > + > OVERFLOW_CHECK(array, sz, max_size); > array = (void *)array + sz; > } > -- > 2.31.1 > >
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