perf(dracut-install): memoize find_kmod_module_from_sysfs_node

find_kmod_module_from_sysfs_node() is called for every platform device
in the system via find_suppliers(). In turn, this calls
kmod_module_new_from_lookup() for every device modalias. This is an
expensive call that reads the modalias files every single time from
scratch.

On many platforms, there are many identical platform devices (e.g.
multiple serial ports, or dozens or hundreds of power domain devices).
Therefore, it's worth memoizing this so we only perform the expensive
lookup once per unique modalias.

This cuts down dracut generation time on an Apple M1 Pro MacBook Pro
from 26 seconds to 17 seconds, give or take (which is close to the
performance prior to 3de4c7313, which introduced a major regression
which has been incrementally improved in prior commits already).

diff --git a/src/install/dracut-install.c b/src/install/dracut-install.c
index e9708c45a507e9e5afcc1d604bf3ed1eb256f558..1862c599df5db0f2d556383b4496f2efac6987e4 100644 (file)
--- a/src/install/dracut-install.c
+++ b/src/install/dracut-install.c
@@ -84,6 +84,7 @@ static Hashmap *items_failed = NULL;
 static Hashmap *modules_loaded = NULL;
 static Hashmap *modules_suppliers = NULL;
 static Hashmap *processed_suppliers = NULL;
+static Hashmap *modalias_to_kmod = NULL;
 static regex_t mod_filter_path;
 static regex_t mod_filter_nopath;
 static regex_t mod_filter_symbol;
@@ -1523,12 +1524,24 @@ static int find_kmod_module_from_sysfs_node(struct kmod_ctx *ctx, const char *sy
         ssize_t len = read(modalias_file, alias, sizeof(alias));
         alias[len - 1] = '\0';
 
-        return kmod_module_new_from_lookup(ctx, alias, modules);
+        void *list;
+
+        if (hashmap_get_exists(modalias_to_kmod, alias, &list) == 1) {
+                *modules = list;
+                return 0;
+        }
+
+        int ret = kmod_module_new_from_lookup(ctx, alias, modules);
+        if (!ret) {
+                hashmap_put(modalias_to_kmod, strdup(alias), *modules);
+        }
+
+        return ret;
 }
 
 static int find_modules_from_sysfs_node(struct kmod_ctx *ctx, const char *sysfs_node, Hashmap *modules)
 {
-        _cleanup_kmod_module_unref_list_ struct kmod_list *list = NULL;
+        struct kmod_list *list = NULL;
         struct kmod_list *l = NULL;
 
         if (find_kmod_module_from_sysfs_node(ctx, sysfs_node, strlen(sysfs_node), &list) >= 0) {
@@ -1585,7 +1598,7 @@ static void find_suppliers(struct kmod_ctx *ctx)
 
         for (FTSENT *ftsent = fts_read(fts); ftsent != NULL; ftsent = fts_read(fts)) {
                 if (strcmp(ftsent->fts_name, "modalias") == 0) {
-                        _cleanup_kmod_module_unref_list_ struct kmod_list *list = NULL;
+                        struct kmod_list *list = NULL;
                         struct kmod_list *l;
 
                         if (find_kmod_module_from_sysfs_node(ctx, ftsent->fts_parent->fts_path, ftsent->fts_parent->fts_pathlen, &list) < 0)
@@ -2197,6 +2210,7 @@ int main(int argc, char **argv)
         items = hashmap_new(string_hash_func, string_compare_func);
         items_failed = hashmap_new(string_hash_func, string_compare_func);
         processed_suppliers = hashmap_new(string_hash_func, string_compare_func);
+        modalias_to_kmod = hashmap_new(string_hash_func, string_compare_func);
 
         if (!items || !items_failed || !processed_suppliers || !modules_loaded) {
                 log_error("Out of memory");
@@ -2270,11 +2284,17 @@ finish2:
         while ((i = hashmap_steal_first(processed_suppliers)))
                 item_free(i);
 
+        /*
+         * Note: modalias_to_kmod's values are freed implicitly by the kmod context destruction
+         * in kmod_unref().
+         */
+
         hashmap_free(items);
         hashmap_free(items_failed);
         hashmap_free(modules_loaded);
         hashmap_free(modules_suppliers);
         hashmap_free(processed_suppliers);
+        hashmap_free(modalias_to_kmod);
 
         if (arg_mod_filter_path)
                 regfree(&mod_filter_path);