tracing: Add hist trigger 'log2' modifier

Allow users to have numeric fields displayed as log2 values in case
value range is very wide by appending '.log2' to field names.

For example,

  # echo 'hist:key=bytes_req' > kmalloc/trigger
  # cat kmalloc/hist

  { bytes_req:        504 } hitcount:          1
  { bytes_req:         11 } hitcount:          1
  { bytes_req:        104 } hitcount:          1
  { bytes_req:         48 } hitcount:          1
  { bytes_req:       2048 } hitcount:          1
  { bytes_req:       4096 } hitcount:          1
  { bytes_req:        240 } hitcount:          1
  { bytes_req:        392 } hitcount:          1
  { bytes_req:         13 } hitcount:          1
  { bytes_req:         28 } hitcount:          1
  { bytes_req:         12 } hitcount:          1
  { bytes_req:         64 } hitcount:          2
  { bytes_req:        128 } hitcount:          2
  { bytes_req:         32 } hitcount:          2
  { bytes_req:          8 } hitcount:         11
  { bytes_req:         10 } hitcount:         13
  { bytes_req:         24 } hitcount:         25
  { bytes_req:        160 } hitcount:         29
  { bytes_req:         16 } hitcount:         33
  { bytes_req:         80 } hitcount:         36

When using '.log2' modifier, the output looks like:

  # echo 'hist:key=bytes_req.log2' > kmalloc/trigger
  # cat kmalloc/hist

  { bytes_req: ~ 2^12 } hitcount:          1
  { bytes_req: ~ 2^11 } hitcount:          1
  { bytes_req: ~ 2^9  } hitcount:          2
  { bytes_req: ~ 2^6  } hitcount:          3
  { bytes_req: ~ 2^3  } hitcount:         13
  { bytes_req: ~ 2^5  } hitcount:         19
  { bytes_req: ~ 2^8  } hitcount:         49
  { bytes_req: ~ 2^7  } hitcount:         57
  { bytes_req: ~ 2^4  } hitcount:         74

Link: http://lkml.kernel.org/r/7ff396b246c6a881f46b979735fddf05a0d6c71a.1457029949.git.tom.zanussi@linux.intel.com

Cc: Tom Zanussi <tom.zanussi@linux.intel.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace.c

@@ -3872,6 +3872,7 @@ static const char readme_msg[] =
 	"\t            .sym-offset display an address as a symbol and offset\n"
 	"\t            .execname   display a common_pid as a program name\n"
 	"\t            .syscall    display a syscall id as a syscall name\n\n"
+	"\t            .log2       display log2 value rather than raw number\n\n"
 	"\t    The 'pause' parameter can be used to pause an existing hist\n"
 	"\t    trigger or to start a hist trigger but not log any events\n"
 	"\t    until told to do so.  'continue' can be used to start or\n"

kernel/trace/trace_events_hist.c

@@ -68,6 +68,13 @@ static u64 hist_field_pstring(struct hist_field *hist_field, void *event)
 	return (u64)(unsigned long)*addr;
 }
 
+static u64 hist_field_log2(struct hist_field *hist_field, void *event)
+{
+	u64 val = *(u64 *)(event + hist_field->field->offset);
+
+	return (u64) ilog2(roundup_pow_of_two(val));
+}
+
 #define DEFINE_HIST_FIELD_FN(type)					\
 static u64 hist_field_##type(struct hist_field *hist_field, void *event)\
 {									\
@@ -111,6 +118,7 @@ enum hist_field_flags {
 	HIST_FIELD_FL_EXECNAME		= 64,
 	HIST_FIELD_FL_SYSCALL		= 128,
 	HIST_FIELD_FL_STACKTRACE	= 256,
+	HIST_FIELD_FL_LOG2		= 512,
 };
 
 struct hist_trigger_attrs {
@@ -358,6 +366,11 @@ static struct hist_field *create_hist_field(struct ftrace_event_field *field,
 		goto out;
 	}
 
+	if (flags & HIST_FIELD_FL_LOG2) {
+		hist_field->fn = hist_field_log2;
+		goto out;
+	}
+
 	if (is_string_field(field)) {
 		flags |= HIST_FIELD_FL_STRING;
 
@@ -522,6 +535,8 @@ static int create_key_field(struct hist_trigger_data *hist_data,
 				flags |= HIST_FIELD_FL_EXECNAME;
 			else if (strcmp(field_str, "syscall") == 0)
 				flags |= HIST_FIELD_FL_SYSCALL;
+			else if (strcmp(field_str, "log2") == 0)
+				flags |= HIST_FIELD_FL_LOG2;
 			else {
 				ret = -EINVAL;
 				goto out;
@@ -980,6 +995,9 @@ hist_trigger_entry_print(struct seq_file *m,
 						      key + key_field->offset,
 						      HIST_STACKTRACE_DEPTH);
 			multiline = true;
+		} else if (key_field->flags & HIST_FIELD_FL_LOG2) {
+			seq_printf(m, "%s: ~ 2^%-2llu", key_field->field->name,
+				   *(u64 *)(key + key_field->offset));
 		} else if (key_field->flags & HIST_FIELD_FL_STRING) {
 			seq_printf(m, "%s: %-50s", key_field->field->name,
 				   (char *)(key + key_field->offset));
@@ -1112,6 +1130,8 @@ static const char *get_hist_field_flags(struct hist_field *hist_field)
 		flags_str = "execname";
 	else if (hist_field->flags & HIST_FIELD_FL_SYSCALL)
 		flags_str = "syscall";
+	else if (hist_field->flags & HIST_FIELD_FL_LOG2)
+		flags_str = "log2";
 
 	return flags_str;
 }