fixdep: use hash table instead of a single array

I noticed fixdep uses ~2% of cpu time in kernel build, in function
use_config()

fixdep spends a lot of cpu cycles in linear searches in its internal
string array. With about 400 stored strings per dep file, this begins to
be noticeable.

Convert fixdep to use a hash table.

kbuild results on my x86_64 allmodconfig

Before patch :

real	10m30.414s
user	61m51.456s
sys	8m28.200s

real	10m12.334s
user	61m50.236s
sys	8m30.448s

real	10m42.947s
user	61m50.028s
sys	8m32.380s

After:

real	10m8.180s
user	61m22.506s
sys	8m32.384s

real	10m35.039s
user	61m21.654s
sys	8m32.212s

real	10m14.487s
user	61m23.498s
sys	8m32.312s

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>

1 files changed, 61 insertions, 48 deletions

diff --git a/scripts/basic/fixdep.c b/scripts/basic/fixdep.c
index ea26b23de08..ed058462369 100644
--- a/scripts/basic/fixdep.c
+++ b/scripts/basic/fixdep.c
@@ -138,38 +138,36 @@ static void print_cmdline(void)
         printf("cmd_%s := %s\n\n", target, cmdline);
 }
 
-char * str_config  = NULL;
-int    size_config = 0;
-int    len_config  = 0;
+struct item {
+        struct item     *next;
+        unsigned int    len;
+        unsigned int    hash;
+        char            name[0];
+};
 
-/*
- * Grow the configuration string to a desired length.
- * Usually the first growth is plenty.
- */
-static void grow_config(int len)
-{
-        while (len_config + len > size_config) {
-                if (size_config == 0)
-                        size_config = 2048;
-                str_config = realloc(str_config, size_config *= 2);
-                if (str_config == NULL)
-                        { perror("fixdep:malloc"); exit(1); }
-        }
-}
+#define HASHSZ 256
+static struct item *hashtab[HASHSZ];
 
+static unsigned int strhash(const char *str, unsigned int sz)
+{
+        /* fnv32 hash */
+        unsigned int i, hash = 2166136261U;
 
+        for (i = 0; i < sz; i++)
+                hash = (hash ^ str[i]) * 0x01000193;
+        return hash;
+}
 
 /*
  * Lookup a value in the configuration string.
  */
-static int is_defined_config(const char * name, int len)
+static int is_defined_config(const char *name, int len, unsigned int hash)
 {
-        const char * pconfig;
-        const char * plast = str_config + len_config - len;
-        for ( pconfig = str_config + 1; pconfig < plast; pconfig++ ) {
-                if (pconfig[ -1] == '\n'
-                &&  pconfig[len] == '\n'
-                &&  !memcmp(pconfig, name, len))
+        struct item *aux;
+
+        for (aux = hashtab[hash % HASHSZ]; aux; aux = aux->next) {
+                if (aux->hash == hash && aux->len == len &&
+                    memcmp(aux->name, name, len) == 0)
                         return 1;
         }
         return 0;
@@ -178,13 +176,19 @@ static int is_defined_config(const char * name, int len)
 /*
  * Add a new value to the configuration string.
  */
-static void define_config(const char * name, int len)
+static void define_config(const char *name, int len, unsigned int hash)
 {
-        grow_config(len + 1);
+        struct item *aux = malloc(sizeof(*aux) + len);
 
-        memcpy(str_config+len_config, name, len);
-        len_config += len;
-        str_config[len_config++] = '\n';
+        if (!aux) {
+                perror("fixdep:malloc");
+                exit(1);
+        }
+        memcpy(aux->name, name, len);
+        aux->len = len;
+        aux->hash = hash;
+        aux->next = hashtab[hash % HASHSZ];
+        hashtab[hash % HASHSZ] = aux;
 }
 
 /*
@@ -192,40 +196,49 @@ static void define_config(const char * name, int len)
  */
 static void clear_config(void)
 {
-        len_config = 0;
-        define_config("", 0);
+        struct item *aux, *next;
+        unsigned int i;
+
+        for (i = 0; i < HASHSZ; i++) {
+                for (aux = hashtab[i]; aux; aux = next) {
+                        next = aux->next;
+                        free(aux);
+                }
+                hashtab[i] = NULL;
+        }
 }
 
 /*
  * Record the use of a CONFIG_* word.
  */
-static void use_config(char *m, int slen)
+static void use_config(const char *m, int slen)
 {
-        char s[PATH_MAX];
-        char *p;
+        unsigned int hash = strhash(m, slen);
+        int c, i;
 
-        if (is_defined_config(m, slen))
+        if (is_defined_config(m, slen, hash))
             return;
 
-        define_config(m, slen);
-
-        memcpy(s, m, slen); s[slen] = 0;
+        define_config(m, slen, hash);
 
-        for (p = s; p < s + slen; p++) {
-                if (*p == '_')
-                        *p = '/';
+        printf("    $(wildcard include/config/");
+        for (i = 0; i < slen; i++) {
+                c = m[i];
+                if (c == '_')
+                        c = '/';
                 else
-                        *p = tolower((int)*p);
+                        c = tolower(c);
+                putchar(c);
         }
-        printf("    $(wildcard include/config/%s.h) \\\n", s);
+        printf(".h) \\\n");
 }
 
-static void parse_config_file(char *map, size_t len)
+static void parse_config_file(const char *map, size_t len)
 {
-        int *end = (int *) (map + len);
+        const int *end = (const int *) (map + len);
         /* start at +1, so that p can never be < map */
-        int *m   = (int *) map + 1;
-        char *p, *q;
+        const int *m   = (const int *) map + 1;
+        const char *p, *q;
 
         for (; m < end; m++) {
                 if (*m == INT_CONF) { p = (char *) m  ; goto conf; }
@@ -265,7 +278,7 @@ static int strrcmp(char *s, char *sub)
         return memcmp(s + slen - sublen, sub, sublen);
 }
 
-static void do_config_file(char *filename)
+static void do_config_file(const char *filename)
 {
         struct stat st;
         int fd;