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Date: Thu, 16 Sep 2021 23:48:31 -0700
From: Stephane Eranian <eranian@...gle.com>
To: Madhavan Srinivasan <maddy@...ux.ibm.com>
Cc: Michael Ellerman <mpe@...erman.id.au>,
Peter Zijlstra <peterz@...radead.org>,
linux-kernel@...r.kernel.org, acme@...hat.com, jolsa@...hat.com,
kim.phillips@....com, namhyung@...nel.org, irogers@...gle.com,
atrajeev@...ux.vnet.ibm.com,
Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: [PATCH v1 01/13] perf/core: add union to struct perf_branch_entry
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@...ux.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@...erman.id.au> wrote:
> >> Michael Ellerman <mpe@...erman.id.au> writes:
> >>> Peter Zijlstra <peterz@...radead.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@...ux.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@...ux.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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