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Subject[PATCH] 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

Signed-off-by: Jean Delvare <>
Cc: Jani Nikula <>
Cc: Daniel Vetter <>
Cc: Rafael J. Wysocki <>
Cc: Jeff Garzik <>
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(-)

--- linux-4.12.orig/drivers/firmware/dmi_scan.c 2017-07-27 08:15:38.283519194 +0200
+++ linux-4.12/drivers/firmware/dmi_scan.c 2017-07-27 08:26:23.013053058 +0200
@@ -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)
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)) {
Jean Delvare
SUSE L3 Support

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