Re: [PATCH v6 2/7] perf/x86/intel: Record branch type

On 4/24/2017 8:47 AM, Jin, Yao wrote:

On 4/23/2017 9:55 PM, Jiri Olsa wrote:

quoted

On Thu, Apr 20, 2017 at 08:07:50PM +0800, Jin Yao wrote:

SNIP

quoted

  +#define X86_BR_TYPE_MAP_MAX    16
+
+static int
+common_branch_type(int type)
+{
+    int i, mask;
+    const int branch_map[X86_BR_TYPE_MAP_MAX] = {
+        PERF_BR_CALL,        /* X86_BR_CALL */
+        PERF_BR_RET,        /* X86_BR_RET */
+        PERF_BR_SYSCALL,    /* X86_BR_SYSCALL */
+        PERF_BR_SYSRET,        /* X86_BR_SYSRET */
+        PERF_BR_INT,        /* X86_BR_INT */
+        PERF_BR_IRET,        /* X86_BR_IRET */
+        PERF_BR_JCC,        /* X86_BR_JCC */
+        PERF_BR_JMP,        /* X86_BR_JMP */
+        PERF_BR_IRQ,        /* X86_BR_IRQ */
+        PERF_BR_IND_CALL,    /* X86_BR_IND_CALL */
+        PERF_BR_NONE,        /* X86_BR_ABORT */
+        PERF_BR_NONE,        /* X86_BR_IN_TX */
+        PERF_BR_NONE,        /* X86_BR_NO_TX */
+        PERF_BR_CALL,        /* X86_BR_ZERO_CALL */
+        PERF_BR_NONE,        /* X86_BR_CALL_STACK */
+        PERF_BR_IND_JMP,    /* X86_BR_IND_JMP */
+    };
+
+    type >>= 2; /* skip X86_BR_USER and X86_BR_KERNEL */
+    mask = ~(~0 << 1);

is that a fancy way to get 1 into the mask? what do I miss?

quoted

+
+    for (i = 0; i < X86_BR_TYPE_MAP_MAX; i++) {
+        if (type & mask)
+            return branch_map[i];

I wonder some bit search would be faster in here, but maybe not big deal

jirka

I just think the branch_map[] doesn't contain many entries (16 entries 
here), so maybe checking 1 bit one time should be acceptable. I just 
want to keep the code simple.

But if the number of entries is more (e.g. 64), maybe it'd better 
check 2 or 4 bits one time.

Thanks
Jin Yao

Hi,

Is this explanation OK? Since for tools part, it's Acked-by: Jiri Olsa. 
I just want to know  if the kernel part is OK either?

Thanks
Jin Yao