PowerPC, P2020RDB, application debug when the application is in tight loop, Sysrq

[saikrishna gajula]

HI All,

             I am new to this group. I am working on Freescale P2020
platform running linux 2.6.21.   I am looking for debug mechanism/utility,
when a multi threaded application running on linux , appears to be hung (
running in a tight loop,deadlock)  while not able to access the board
through serial/SSH/Telnet.

   I was looking at Magic sysrq option in linux to generate the stack,
register dump when the application is hung. I am able to dump the call
trace in normal working conditions. But i can't use  echo  t >
/proc/sysrq-trigger and debug when the application hung.

 I am using below piece of code(drivers/serial/8250.c) on P2020RDB to debug
the application where in , in hung situation, when i press 'y'  followed by
't'  on serial console it should go to sysrq handler, and dump the call
trace, but it is not happening.(simply board hung)

{
           if(sysrq_enable_flag)
                  handle_sysrq(ch, up->port.info->tty);

        sysrq_enable_flag = 0;

        if(ch == 'y')
            sysrq_enable_flag = 1;
}

It would be helpful if you provide any hint on the issue, or any other way
to debug the application in hang situations.

Thanks,
Sai


On Tue, Apr 16, 2013 at 9:24 PM, Anshuman Khandual <
khandual at linux.vnet.ibm.com> wrote:

>                 Branch History Rolling Buffer (BHRB) is a new PMU feaure
> in IBM
> POWER8 processor which records the branch instructions inside the execution
> pipeline. This patchset enables the basic functionality of the feature
> through
> generic perf branch stack sampling framework.
>
> Sample output
> -------------
> $./perf record -b top
> $./perf report
>
> Overhead  Command  Source Shared Object                           Source
> Symbol  Target Shared Object                        Target Symbol
> # ........  .......  ....................
>  ......................................  ....................
>  ...................................
> #
>
>      7.82%      top  libc-2.11.2.so        [k] _IO_vfscanf
>           libc-2.11.2.so        [k] _IO_vfscanf
>      6.17%      top  libc-2.11.2.so        [k] _IO_vfscanf
>           [unknown]             [k] 00000000
>      2.37%      top  [unknown]             [k] 0xf7aafb30
>          [unknown]             [k] 00000000
>      1.80%      top  [unknown]             [k] 0x0fe07978
>          libc-2.11.2.so        [k] _IO_vfscanf
>      1.60%      top  libc-2.11.2.so        [k] _IO_vfscanf
>           [kernel.kallsyms]     [k] .do_task_stat
>      1.20%      top  [kernel.kallsyms]     [k] .do_task_stat
>         [kernel.kallsyms]     [k] .do_task_stat
>      1.02%      top  libc-2.11.2.so        [k] vfprintf
>          libc-2.11.2.so        [k] vfprintf
>      0.92%      top  top                   [k] _init
>         [unknown]             [k] 0x0fe037f4
>
> Changes in V2
> --------------
> - Added copyright messages to the newly created files
> - Modified couple of commit messages
>
> Anshuman Khandual (5):
>   powerpc, perf: Add new BHRB related instructions on POWER8
>   powerpc, perf: Add basic assembly code to read BHRB entries on POWER8
>   powerpc, perf: Add new BHRB related generic functions, data and flags
>   powerpc, perf: Define BHRB generic functions, data and flags for POWER8
>   powerpc, perf: Enable branch stack sampling framework support with BHRB
>
>  arch/powerpc/include/asm/perf_event_server.h |  6 ++
>  arch/powerpc/include/asm/ppc-opcode.h        |  7 ++
>  arch/powerpc/perf/Makefile                   |  2 +-
>  arch/powerpc/perf/bhrb.S                     | 44 +++++++++++++
>  arch/powerpc/perf/core-book3s.c              | 96
> +++++++++++++++++++++++++++-
>  arch/powerpc/perf/perf_event_bhrb.c          | 85 ++++++++++++++++++++++++
>  arch/powerpc/perf/power8-pmu.c               | 57 ++++++++++++++++-
>  7 files changed, 292 insertions(+), 5 deletions(-)
>  create mode 100644 arch/powerpc/perf/bhrb.S
>  create mode 100644 arch/powerpc/perf/perf_event_bhrb.c
>
> --
> 1.7.11.7
>
> _______________________________________________
> Linuxppc-dev mailing list
> Linuxppc-dev at lists.ozlabs.org
> https://lists.ozlabs.org/listinfo/linuxppc-dev
>
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