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SubjectRe: Strange reports of perf events on powerpc 83xx
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Le 02/09/2015 16:20, Joakim Tjernlund a écrit :
> On Thu, 2015-08-27 at 15:58 +0200, leroy christophe wrote:
>> Hi,
>>
>> Has anybody already used 'perf' tool on powerpc MPC83xx ?
>>
>> I have been succesfully using perf on MPC8xx, but on MPC83xx I get
>> something strange.
>>
>> perf record/report reports addresses on user stack, as if it was mixing
>> up D accesses and I accesses.
>>
>> Any idea of what the problem can be ?
> We are also experiencing strange addresses on 83xx, did find the cause
> of this problem?
>
> We are using Linux 4.1.0
I identified this afternoon that the issue comes from
perf_instruction_pointer()
which reads SPRN_SIAR instead of using the NIP register from the pt_regs
struct
According to the MPC8323 reference manual, there is no such register.

I'm looking at the history in order to fully understand the reason.
Looks like PPC_HAVE_PMU_SUPPORT is selected for all PPC_BOOK3S_32 allthought
mpc832x has no PMU.

Christophe
>
>> # Samples: 8K of event 'cpu-clock'
>> # Event count (approx.): 2196000000
>> #
>> # Overhead Command Shared Object Symbol
>> # ........ ............ ..................
>> ............................................
>> #
>> 2.62% perf_reseau4 libpthread-2.18.so [.] __libc_send
>> 2.56% perf_reseau4 [kernel.kallsyms] [k] __ip_make_skb
>> 1.62% perf_reseau4 [kernel.kallsyms] [k] __ip_append_data.isra.39
>> 1.55% perf_reseau4 [kernel.kallsyms] [k] ip_finish_output
>> 1.33% perf_reseau4 [unknown] [k] 0x7ffffd94
>> 1.33% perf_reseau4 [unknown] [k] 0x7ffffd95
>> 1.28% perf_reseau4 [unknown] [k] 0x7ffffd97
>> 1.26% perf_reseau4 [unknown] [k] 0x7ffffda3
>> 1.24% perf_reseau4 [unknown] [k] 0x7ffffd98
>> 1.22% perf_reseau4 [unknown] [k] 0x7ffffd92
>> 1.22% perf_reseau4 [unknown] [k] 0x7ffffd9b
>> 1.22% perf_reseau4 [unknown] [k] 0x7ffffdaa
>> 1.21% perf_reseau4 [unknown] [k] 0x7ffffd96
>> 1.18% perf_reseau4 [unknown] [k] 0x7ffffda7
>> 1.17% perf_reseau4 [unknown] [k] 0x7ffffd8d
>> 1.17% perf_reseau4 [unknown] [k] 0x7ffffd99
>> 1.13% perf_reseau4 [unknown] [k] 0x7ffffd90
>> 1.13% perf_reseau4 [unknown] [k] 0x7ffffda2
>> 1.12% perf_reseau4 [kernel.kallsyms] [k] __local_bh_enable_ip
>> 1.12% perf_reseau4 [unknown] [k] 0x7ffffd9c
>> 1.12% perf_reseau4 [unknown] [k] 0x7ffffd9e
>> 1.10% perf_reseau4 [unknown] [k] 0x7ffffda0
>> 1.08% perf_reseau4 [unknown] [k] 0x7ffffd9f
>> 1.08% perf_reseau4 [unknown] [k] 0x7ffffda6
>> 1.05% perf_reseau4 [unknown] [k] 0x7ffffda8
>> 1.02% perf_reseau4 [unknown] [k] 0x7ffffd9a
>> 1.01% perf_reseau4 [unknown] [k] 0x7ffffdb0
>> 1.00% perf_reseau4 [unknown] [k] 0x7ffffd89
>> 1.00% perf_reseau4 [unknown] [k] 0x7ffffd8b
>> 1.00% perf_reseau4 [unknown] [k] 0x7ffffdac


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