Re: Strange reports of perf events on powerpc 83xx

From: christophe leroy
Date: Wed Sep 02 2015 - 14:49:07 EST

Le 02/09/2015 16:20, Joakim Tjernlund a écrit :
On Thu, 2015-08-27 at 15:58 +0200, leroy christophe wrote:

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.


# Samples: 8K of event 'cpu-clock'
# Event count (approx.): 2196000000
# Overhead Command Shared Object Symbol
# ........ ............ ..................
2.62% perf_reseau4 [.] __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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