diff --git a/tools/perf/util/string.c b/tools/perf/util/string.c
index 2553e5b55b8996175220d8fc16cfb403161f35b7..d87767f76903e17f2e59a93ad36bc6e6b2f2e6a0 100644
--- a/tools/perf/util/string.c
+++ b/tools/perf/util/string.c
@@ -9,78 +9,48 @@
  */
 s64 perf_atoll(const char *str)
 {
-	unsigned int i;
-	s64 length = -1, unit = 1;
+	s64 length;
+	char *p;
+	char c;
 
 	if (!isdigit(str[0]))
 		goto out_err;
 
-	for (i = 1; i < strlen(str); i++) {
-		switch (str[i]) {
-		case 'B':
-		case 'b':
-			break;
-		case 'K':
-			if (str[i + 1] != 'B')
-				goto out_err;
-			else
-				goto kilo;
-		case 'k':
-			if (str[i + 1] != 'b')
-				goto out_err;
-kilo:
-			unit = K;
-			break;
-		case 'M':
-			if (str[i + 1] != 'B')
-				goto out_err;
-			else
-				goto mega;
-		case 'm':
-			if (str[i + 1] != 'b')
+	length = strtoll(str, &p, 10);
+	switch (c = *p++) {
+		case 'b': case 'B':
+			if (*p)
 				goto out_err;
-mega:
-			unit = K * K;
+		case '\0':
+			return length;
+		default:
+			goto out_err;
+		/* two-letter suffices */
+		case 'k': case 'K':
+			length <<= 10;
 			break;
-		case 'G':
-			if (str[i + 1] != 'B')
-				goto out_err;
-			else
-				goto giga;
-		case 'g':
-			if (str[i + 1] != 'b')
-				goto out_err;
-giga:
-			unit = K * K * K;
+		case 'm': case 'M':
+			length <<= 20;
 			break;
-		case 'T':
-			if (str[i + 1] != 'B')
-				goto out_err;
-			else
-				goto tera;
-		case 't':
-			if (str[i + 1] != 'b')
-				goto out_err;
-tera:
-			unit = K * K * K * K;
+		case 'g': case 'G':
+			length <<= 30;
 			break;
-		case '\0':	/* only specified figures */
-			unit = 1;
+		case 't': case 'T':
+			length <<= 40;
 			break;
-		default:
-			if (!isdigit(str[i]))
-				goto out_err;
-			break;
-		}
 	}
-
-	length = atoll(str) * unit;
-	goto out;
+	/* we want the cases to match */
+	if (islower(c)) {
+		if (strcmp(p, "b") != 0)
+			goto out_err;
+	} else {
+		if (strcmp(p, "B") != 0)
+			goto out_err;
+	}
+	return length;
 
 out_err:
-	length = -1;
-out:
-	return length;
+	return -1;
 }
 
 /*