Re: [PATCH V2 1/5] perf/core: Add PERF_SAMPLE_WEIGHT_STRUCT

[Liang, Kan]

On 1/27/2021 2:03 PM, Peter Zijlstra wrote:
On Wed, Jan 27, 2021 at 07:38:41AM -0800, kan.li...@linux.intel.com wrote:
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index b15e344..13b4019 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -145,12 +145,14 @@ enum perf_event_sample_format {
        PERF_SAMPLE_CGROUP                      = 1U << 21,
        PERF_SAMPLE_DATA_PAGE_SIZE              = 1U << 22,
        PERF_SAMPLE_CODE_PAGE_SIZE              = 1U << 23,
+       PERF_SAMPLE_WEIGHT_STRUCT               = 1U << 24,
  
-	PERF_SAMPLE_MAX = 1U << 24,		/* non-ABI */
+       PERF_SAMPLE_MAX = 1U << 25,               /* non-ABI */
  
  	__PERF_SAMPLE_CALLCHAIN_EARLY		= 1ULL << 63, /* non-ABI; internal use */
  };
  
+#define PERF_SAMPLE_WEIGHT_TYPE	(PERF_SAMPLE_WEIGHT | PERF_SAMPLE_WEIGHT_STRUCT)
  /*
   * values to program into branch_sample_type when PERF_SAMPLE_BRANCH is set
   *
@@ -890,7 +892,16 @@ enum perf_event_type {
         *        char                  data[size];
         *        u64                   dyn_size; } && PERF_SAMPLE_STACK_USER
         *
-        *      { u64                   weight;   } && PERF_SAMPLE_WEIGHT
+        *      { union perf_sample_weight
+        *       {
+        *              u64             full; && PERF_SAMPLE_WEIGHT
+        *              struct {
+        *                      u32     low_dword;
+        *                      u16     high_word;
+        *                      u16     higher_word;
+        *              } && PERF_SAMPLE_WEIGHT_STRUCT
+        *       }
+        *      }
         *      { u64                   data_src; } && PERF_SAMPLE_DATA_SRC
         *      { u64                   transaction; } && 
PERF_SAMPLE_TRANSACTION
         *      { u64                   abi; # enum perf_sample_regs_abi
@@ -1248,4 +1259,13 @@ struct perf_branch_entry {
                reserved:40;
  };
  
+union perf_sample_weight {
+       __u64           full;
+       struct {
+               __u32   low_dword;
+               __u16   high_word;
+               __u16   higher_word;
+       };
+};

*urgh*, my naming lives ... anybody got a better suggestion?

I think we need a generic name here, but the problem is that the 
'weight' field has different meanings among architectures.

The 'weight' fields are to store all kinds of latency on X86.
On PowerPC, it stores MMCRA[TECX/TECM], which doesn't look like a latency.

I don't think I can use the name, 'cache_lat' or 'instruction_lat', 
here. Right?
If so, how about 'var'?

u32 var_1_dw;
u16 var_2_w;
u16 var_3_w;



Also, do we want to care about byte order?

Sure. I will add the big-endian and little-endian support.


Thanks,
Kan