firmware: dmi: Optimize dmi_matches

Function dmi_matches can me made a bit faster:

* The documented purpose of dmi_initialized is to catch too early calls to dmi_check_system(). I'm not fully convinced it justifies slowing down the initialization of all systems out there, but at least the check should not have been moved from dmi_check_system() to dmi_matches(). dmi_matches() is being called for every entry of the table passed to dmi_check_system(), causing the same redundant check to be performed again and again. So move it back to dmi_check_system(), reverting this specific portion of commit d7b1956fed33 ("DMI: Introduce dmi_first_match to make the interface more flexible").

* Don't check for the exact_match flag again when we already know its value.

---
Regarding dmi_initialized, I don't think it makes sense to check for a possible bad initialization order at run time on every system when it is all decided at build time. If a developer introduces a new call to dmi_check_system() and it is too early in the initialization sequence, I believe he/she would notice upon first testing, and a comment to his/her intention in the source code would serve the same purpose without the worldwide performance penalty. Would anyone object to such a change?

 drivers/firmware/dmi_scan.c |   19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

@@ -784,19 +784,20 @@ static bool dmi_matches(const struct dmi
 {
 	int i;
 
-	WARN(!dmi_initialized, KERN_ERR "dmi check: not initialized yet.\n");
-
 	for (i = 0; i < ARRAY_SIZE(dmi->matches); i++) {
 		int s = dmi->matches[i].slot;
 		if (s == DMI_NONE)
 			break;
 		if (dmi_ident[s]) {
-			if (!dmi->matches[i].exact_match &&
-			    strstr(dmi_ident[s], dmi->matches[i].substr))
-				continue;
-			else if (dmi->matches[i].exact_match &&
-				 !strcmp(dmi_ident[s], dmi->matches[i].substr))
-				continue;
+			if (dmi->matches[i].exact_match) {
+				if (!strcmp(dmi_ident[s],
+					    dmi->matches[i].substr))
+					continue;
+			} else {
+				if (strstr(dmi_ident[s],
+					   dmi->matches[i].substr))
+					continue;
+			}
 		}
 
 		/* No match */

@@ -832,6 +833,8 @@ int dmi_check_system(const struct dmi_sy
 	int count = 0;
 	const struct dmi_system_id *d;
 
+	WARN(!dmi_initialized, KERN_ERR "dmi check: not initialized yet.\n");
+
 	for (d = list; !dmi_is_end_of_table(d); d++)
 		if (dmi_matches(d)) {
 			count++;

Jean Delvare
SUSE L3 Support