From: Michael Ellerman <mpe@ellerman.id.au>
To: Peter Zijlstra <peterz@infradead.org>,
Stephane Eranian <eranian@google.com>
Cc: linux-kernel@vger.kernel.org, acme@redhat.com, jolsa@redhat.com,
kim.phillips@amd.com, namhyung@kernel.org, irogers@google.com,
atrajeev@linux.vnet.ibm.com, maddy@linux.ibm.com
Subject: Re: [PATCH v1 01/13] perf/core: add union to struct perf_branch_entry
Date: Sat, 11 Sep 2021 00:16:20 +1000 [thread overview]
Message-ID: <875yv8ms7f.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <878s04my3b.fsf@mpe.ellerman.id.au>
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 :/
cheers
next prev parent reply other threads:[~2021-09-10 14:16 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-09 7:56 [PATCH v1 00/13] perf/x86/amd: Add AMD Fam19h Branch Sampling support Stephane Eranian
2021-09-09 7:56 ` [PATCH v1 01/13] perf/core: add union to struct perf_branch_entry Stephane Eranian
2021-09-09 19:03 ` Peter Zijlstra
2021-09-10 12:09 ` Michael Ellerman
2021-09-10 14:16 ` Michael Ellerman [this message]
2021-09-15 6:03 ` Stephane Eranian
2021-09-17 6:37 ` Madhavan Srinivasan
2021-09-17 6:48 ` Stephane Eranian
2021-09-17 7:05 ` Michael Ellerman
2021-09-17 7:39 ` Stephane Eranian
2021-09-17 12:38 ` Michael Ellerman
2021-09-17 16:42 ` Stephane Eranian
2021-09-19 10:27 ` Michael Ellerman
2021-09-09 7:56 ` [PATCH v1 02/13] x86/cpufeatures: add AMD Fam19h Branch Sampling feature Stephane Eranian
2021-09-09 7:56 ` [PATCH v1 03/13] perf/x86/amd: add AMD Fam19h Branch Sampling support Stephane Eranian
2021-09-09 10:44 ` kernel test robot
2021-09-09 15:33 ` kernel test robot
2021-09-09 7:56 ` [PATCH v1 04/13] perf/x86/amd: add branch-brs helper event for Fam19h BRS Stephane Eranian
2021-09-09 7:56 ` [PATCH v1 05/13] perf/x86/amd: enable branch sampling priv level filtering Stephane Eranian
2021-09-09 7:56 ` [PATCH v1 06/13] perf/x86/amd: add AMD branch sampling period adjustment Stephane Eranian
2021-09-09 7:56 ` [PATCH v1 07/13] perf/core: add idle hooks Stephane Eranian
2021-09-09 9:15 ` Peter Zijlstra
2021-09-09 10:42 ` kernel test robot
2021-09-09 11:02 ` kernel test robot
2021-09-09 7:56 ` [PATCH v1 08/13] perf/x86/core: " Stephane Eranian
2021-09-09 9:16 ` Peter Zijlstra
2021-09-09 7:56 ` [PATCH v1 09/13] perf/x86/amd: add idle hooks for branch sampling Stephane Eranian
2021-09-09 9:20 ` Peter Zijlstra
2021-09-09 7:56 ` [PATCH v1 10/13] perf tools: add branch-brs as a new event Stephane Eranian
2021-09-09 7:56 ` [PATCH v1 11/13] perf tools: improve IBS error handling Stephane Eranian
2021-09-13 19:34 ` Arnaldo Carvalho de Melo
2021-10-04 21:57 ` Kim Phillips
2021-10-04 23:44 ` Arnaldo Carvalho de Melo
2021-09-09 7:56 ` [PATCH v1 12/13] perf tools: improve error handling of AMD Branch Sampling Stephane Eranian
2021-10-04 21:57 ` Kim Phillips
2021-09-09 7:57 ` [PATCH v1 13/13] perf report: add addr_from/addr_to sort dimensions Stephane Eranian
2021-09-09 8:55 ` [PATCH v1 00/13] perf/x86/amd: Add AMD Fam19h Branch Sampling support Peter Zijlstra
2021-09-15 5:55 ` Stephane Eranian
2021-09-15 9:04 ` Peter Zijlstra
2021-10-28 18:30 ` Stephane Eranian
2021-09-27 20:17 ` Song Liu
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