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Re: [PATCH v3 1/6] powerpc/perf: Define big-endian version of perf_mem_data_src

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On Tue, Apr 11, 2017 at 07:21:05AM +0530, Madhavan Srinivasan wrote:
> From: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
> 
> perf_mem_data_src is an union that is initialized via the ->val field
> and accessed via the bitmap fields. For this to work on big endian
> platforms (Which is broken now), we also need a big-endian represenation
> of perf_mem_data_src. i.e, in a big endian system, if user request
> PERF_SAMPLE_DATA_SRC (perf report -d), will get the default value from
> perf_sample_data_init(), which is PERF_MEM_NA. Value for PERF_MEM_NA
> is constructed using shifts:
> 
>   /* TLB access */
>   #define PERF_MEM_TLB_NA		0x01 /* not available */
>   ...
>   #define PERF_MEM_TLB_SHIFT	26
> 
>   #define PERF_MEM_S(a, s) \
> 	(((__u64)PERF_MEM_##a##_##s) << PERF_MEM_##a##_SHIFT)
> 
>   #define PERF_MEM_NA (PERF_MEM_S(OP, NA)   |\
> 		    PERF_MEM_S(LVL, NA)   |\
> 		    PERF_MEM_S(SNOOP, NA) |\
> 		    PERF_MEM_S(LOCK, NA)  |\
> 		    PERF_MEM_S(TLB, NA))
> 
> Which works out as:
> 
>   ((0x01 << 0) | (0x01 << 5) | (0x01 << 19) | (0x01 << 24) | (0x01 << 26))
> 
> Which means the PERF_MEM_NA value comes out of the kernel as 0x5080021
> in CPU endian.
> 
> But then in the perf tool, the code uses the bitfields to inspect the
> value, and currently the bitfields are defined using little endian
> ordering.
> 
> So eg. in perf_mem__tlb_scnprintf() we see:
>   data_src->val = 0x5080021
>              op = 0x0
>             lvl = 0x0
>           snoop = 0x0
>            lock = 0x0
>            dtlb = 0x0
>            rsvd = 0x5080021
> 
> Patch does a minimal fix of adding big endian definition of the bitfields
> to match the values that are already exported by the kernel on big endian.
> And it makes no change on little endian.

I think it is important to note that there are no current big-endian
users. So 'fixing' this will not break anybody and will ensure future
users (next patch) will work correctly.

Aside from that amendment,

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

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[PATCH v3 0/6] powerpc/perf: Export memory hierarchy level Madhavan Srinivasan <maddy@linux.vnet.ibm.com> - 2017-04-11 04:00 +0200
  [PATCH v3 4/6] powerpc/perf: Support to export SIERs bit in Power8 Madhavan Srinivasan <maddy@linux.vnet.ibm.com> - 2017-04-11 04:00 +0200
  [PATCH v3 5/6] powerpc/perf: Support to export SIERs bit in Power9 Madhavan Srinivasan <maddy@linux.vnet.ibm.com> - 2017-04-11 04:00 +0200
  [PATCH v3 6/6] powerpc/perf: Add Power8 mem_access event to sysfs Madhavan Srinivasan <maddy@linux.vnet.ibm.com> - 2017-04-11 04:00 +0200
  [PATCH v3 1/6] powerpc/perf: Define big-endian version of perf_mem_data_src Madhavan Srinivasan <maddy@linux.vnet.ibm.com> - 2017-04-11 04:00 +0200
    Re: [PATCH v3 1/6] powerpc/perf: Define big-endian version of  perf_mem_data_src Peter Zijlstra <peterz@infradead.org> - 2017-04-13 14:40 +0200
      Re: [PATCH v3 1/6] powerpc/perf: Define big-endian version of perf_mem_data_src Michael Ellerman <mpe@ellerman.id.au> - 2017-04-13 15:30 +0200
        Re: [PATCH v3 1/6] powerpc/perf: Define big-endian version of  perf_mem_data_src Madhavan Srinivasan <maddy@linux.vnet.ibm.com> - 2017-04-17 05:50 +0200
      Re: [PATCH v3 1/6] powerpc/perf: Define big-endian version of  perf_mem_data_src Madhavan Srinivasan <maddy@linux.vnet.ibm.com> - 2017-04-17 05:50 +0200
      Re: [PATCH v3 1/6] powerpc/perf: Define big-endian version of perf_mem_data_src Michael Ellerman <mpe@ellerman.id.au> - 2017-04-19 07:00 +0200
        Re: [PATCH v3 1/6] powerpc/perf: Define big-endian version of  perf_mem_data_src Madhavan Srinivasan <maddy@linux.vnet.ibm.com> - 2017-04-19 16:50 +0200
          Re: [PATCH v3 1/6] powerpc/perf: Define big-endian version of perf_mem_data_src Michael Ellerman <mpe@ellerman.id.au> - 2017-04-20 00:20 +0200
    Re: [v3, 1/6] powerpc/perf: Define big-endian version of perf_mem_data_src Michael Ellerman <patch-notifications@ellerman.id.au> - 2017-04-20 00:10 +0200
  [PATCH v3 3/6] powerpc/perf: Support to export MMCRA[TEC*] field to userspace Madhavan Srinivasan <maddy@linux.vnet.ibm.com> - 2017-04-11 04:00 +0200

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