[RFC PATCH] lib/access.c optimization

[mhoffman at lightlink.com (Mark M. Hoffman)]

Hi:

The following patch shaves about 8% off the execution time of 'sensors -u'
on my workstation (2645586 cycles before vs. 2430821 cycles after).

Can I please get an ACK on this patch before I commit it?  Thanks.

Measurement method:
	(build/install lm-sensors userspace with DEBUG=1 to get -g)
	valgrind --tool=callgrind sensors -u
	kcachegrind callgrind.out.NNNN


Index: lib/access.c
===================================================================
--- lib/access.c	(revision 4073)
+++ lib/access.c	(working copy)
@@ -84,22 +84,44 @@
 	return NULL;
 }
 
+static const sensors_chip_feature *sensors_lookup_features(const char *prefix)
+{
+	static int cache = 0;
+	int ii = cache;
+
+	if (!strcasecmp(sensors_chip_features_list[ii].prefix, prefix))
+		return sensors_chip_features_list[ii].feature;
+
+	for (ii = 0; sensors_chip_features_list[ii].prefix; ii++)
+		if (!strcasecmp(sensors_chip_features_list[ii].prefix, prefix)){
+			cache = ii;
+			return sensors_chip_features_list[ii].feature;
+		}
+
+	return NULL;
+}
+
 /* Look up a resource in the intern chip list, and return a pointer to it. 
    Do not modify the struct the return value points to! Returns NULL if 
    not found.*/
 const sensors_chip_feature *sensors_lookup_feature_nr(const char *prefix,
 						      int feature)
 {
-	int i, j;
-	const sensors_chip_feature *features;
+	static int cache = 0;
+	int ii = cache;
+	const sensors_chip_feature *features = sensors_lookup_features(prefix);
 
-	for (i = 0; sensors_chip_features_list[i].prefix; i++)
-		if (!strcasecmp(sensors_chip_features_list[i].prefix, prefix)) {
-			features = sensors_chip_features_list[i].feature;
-			for (j = 0; features[j].name; j++)
-				if (features[j].number == feature)
-					return features + j;
-		}
+	if (features) {
+		if (features[ii].number == feature)
+			return features + ii;
+
+		for (ii = 0; features[ii].name; ii++)
+			if (features[ii].number == feature) {
+				cache = ii;
+				return features + ii;
+			}
+
+	}
 	return NULL;
 }
 
@@ -109,16 +131,20 @@
 const sensors_chip_feature *sensors_lookup_feature_name(const char *prefix,
 							const char *feature)
 {
-	int i, j;
-	const sensors_chip_feature *features;
+	static int cache = 0;
+	int ii = cache;
+	const sensors_chip_feature *features = sensors_lookup_features(prefix);
 
-	for (i = 0; sensors_chip_features_list[i].prefix; i++)
-		if (!strcasecmp(sensors_chip_features_list[i].prefix, prefix)) {
-			features = sensors_chip_features_list[i].feature;
-			for (j = 0; features[j].name; j++)
-				if (!strcasecmp(features[j].name, feature))
-					return features + j;
-		}
+	if (features) {
+		if (!strcasecmp(features[ii].name, feature))
+			return features + ii;
+
+		for (ii = 0; features[ii].name; ii++)
+			if (!strcasecmp(features[ii].name, feature)) {
+				cache = ii;
+				return features + ii;
+			}
+	}
 	return NULL;
 }
 
@@ -329,33 +355,36 @@
 const sensors_feature_data *sensors_get_all_features(sensors_chip_name name,
 						     int *nr1, int *nr2)
 {
-	sensors_chip_feature *feature_list;
-	int i;
+	const sensors_chip_feature *feature_list =
+				sensors_lookup_features(name.prefix);
 
-	for (i = 0; sensors_chip_features_list[i].prefix; i++)
-		if (!strcasecmp(sensors_chip_features_list[i].prefix, name.prefix)) {
-			feature_list = sensors_chip_features_list[i].feature;
-			if (!*nr1 && !*nr2) {	/* Return the first entry */
-				if (!feature_list[0].name)	/* The list may be empty */
-					return NULL;
-				*nr1 = *nr2 = 1;
-				return (sensors_feature_data *)feature_list;
-			}
-			for ((*nr2)++; feature_list[*nr2 - 1].name; (*nr2)++)
-				if (feature_list[*nr2 - 1].logical_mapping ==
-				    feature_list[*nr1 - 1].number)
-					return (sensors_feature_data *)
-						(feature_list + *nr2 - 1);
-			for ((*nr1)++;
-			     feature_list[*nr1 - 1].name
-			     && (feature_list[*nr1 - 1].logical_mapping !=
-				 SENSORS_NO_MAPPING); (*nr1)++) ;
-			*nr2 = *nr1;
-			if (!feature_list[*nr1 - 1].name)
-				return NULL;
-			return (sensors_feature_data *)(feature_list + *nr1 - 1);
-		}
-	return NULL;
+	if (!feature_list)
+		return NULL;
+
+	/* Return the first entry */
+	if (!*nr1 && !*nr2) {
+
+		/* The list may be empty */
+		if (!feature_list[0].name)
+			return NULL;
+
+		*nr1 = *nr2 = 1;
+		return (sensors_feature_data *)feature_list;
+	}
+
+	for ((*nr2)++; feature_list[*nr2 - 1].name; (*nr2)++)
+		if (feature_list[*nr2 - 1].logical_mapping ==
+					feature_list[*nr1 - 1].number)
+			return (sensors_feature_data *)(feature_list + *nr2 - 1);
+
+	for ((*nr1)++; feature_list[*nr1 - 1].name &&
+		(feature_list[*nr1 - 1].logical_mapping != SENSORS_NO_MAPPING);
+		(*nr1)++) ;
+
+	*nr2 = *nr1;
+	if (!feature_list[*nr1 - 1].name)
+		return NULL;
+	return (sensors_feature_data *)(feature_list + *nr1 - 1);
 }
 
 int sensors_eval_expr(sensors_chip_name chipname, const sensors_expr * expr,
-- 
Mark M. Hoffman
mhoffman at lightlink.com