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Message-ID: <b21bf42e-377d-36d0-49c3-af1e4edf5496@linux.ibm.com>
Date: Fri, 17 Sep 2021 12:07:50 +0530
From: Madhavan Srinivasan <maddy@...ux.ibm.com>
To: Stephane Eranian <eranian@...gle.com>,
Michael Ellerman <mpe@...erman.id.au>
Cc: 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
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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