perf expr: Add d_ratio operation

d_ratio avoids division by 0 yielding infinity, such as when a counter
doesn't get scheduled. An example usage is:

  {
      "BriefDescription": "DCache L1 misses",
      "MetricExpr": "d_ratio(MEM_LOAD_RETIRED.L1_MISS, MEM_LOAD_RETIRED.L1_HIT + MEM_LOAD_RETIRED.L1_MISS + MEM_LOAD_RETIRED.FB_HIT)",
      "MetricGroup": "DCache;DCache_L1",
      "MetricName": "DCache_L1_Miss",
      "ScaleUnit": "100%",
  }
Signed-off-by: Ian Rogers <irogers@google.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: John Garry <john.garry@huawei.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Clarke <pc@us.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20200610235823.52557-1-irogers@google.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/expr.c

@@ -39,6 +39,8 @@ int test__expr(struct test *t __maybe_unused, int subtest __maybe_unused)
 	ret |= test(&ctx, "1+1 if 3*4 else 0", 2);
 	ret |= test(&ctx, "1.1 + 2.1", 3.2);
 	ret |= test(&ctx, ".1 + 2.", 2.1);
+	ret |= test(&ctx, "d_ratio(1, 2)", 0.5);
+	ret |= test(&ctx, "d_ratio(2.5, 0)", 0);
 
 	if (ret)
 		return ret;

tools/perf/util/expr.l

@@ -100,6 +100,7 @@ symbol		({spec}|{sym})+
 		}
 	}
 
+d_ratio		{ return D_RATIO; }
 max		{ return MAX; }
 min		{ return MIN; }
 if		{ return IF; }

tools/perf/util/expr.y

@@ -10,6 +10,14 @@
 #include "smt.h"
 #include <string.h>
 
+static double d_ratio(double val0, double val1)
+{
+	if (val1 == 0) {
+		return 0;
+	}
+	return  val0 / val1;
+}
+
 %}
 
 %define api.pure full
@@ -28,7 +36,7 @@
 %token <num> NUMBER
 %token <str> ID
 %destructor { free ($$); } <str>
-%token MIN MAX IF ELSE SMT_ON
+%token MIN MAX IF ELSE SMT_ON D_RATIO
 %left MIN MAX IF
 %left '|'
 %left '^'
@@ -64,7 +72,8 @@ other: ID
 }
 |
 MIN | MAX | IF | ELSE | SMT_ON | NUMBER | '|' | '^' | '&' | '-' | '+' | '*' | '/' | '%' | '(' | ')' | ','
-
+|
+D_RATIO
 
 all_expr: if_expr			{ *final_val = $1; }
 	;
@@ -105,6 +114,7 @@ expr:	  NUMBER
 	| MIN '(' expr ',' expr ')' { $$ = $3 < $5 ? $3 : $5; }
 	| MAX '(' expr ',' expr ')' { $$ = $3 > $5 ? $3 : $5; }
 	| SMT_ON		 { $$ = smt_on() > 0; }
+	| D_RATIO '(' expr ',' expr ')' { $$ = d_ratio($3,$5); }
 	;
 
 %%