Re: Strange reports of perf events on powerpc 83xx

[christophe leroy]

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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