cache performance boost for recursion + cleanup + xmalloc

robang74 · robang74 · commit 2cbc9640f8b6 · 2026-04-09T16:46:44.000+02:00
Status: patch applies cleanly apart concat_path_file_fast() manually added From 69312a6928c188ac8be3c714db3a53724b85dd09 Mon Sep 17 00:00:00 2001 From: Jody Bruchon <jody@jodybruchon.com> Date: Wed, 10 Apr 2024 18:08:00 -0400 Subject: [PATCH v2] Huge performance boost for recursion (cp, du, find, ls, rm, mv) This patch uses pre-calculated name lengths to massively speed up various recursive operations. Three new *_fast variant functions are added along with get_d_namlen copied from libjodycode. Passing lengths allows use of memcpy() instead of strcpy()/strcat() and replacement of a particularly hot xasprintf(). Cachegrind shows CPU instructions on Linux x86_64 drop by 24% to 67% with similar reductions in data reads and writes. Anything in BusyBox that uses a while(readdir()) loop or that calls concat_*path_file() or last_char_is() might benefit from adopting this optimization framework. Bloat-O-Meter: function old new delta concat_path_file_fast - 194 +194 get_d_namlen - 36 +36 concat_subpath_file_fast - 31 +31 last_char_is_fast - 26 +26 complete_cmd_dir_file 992 1002 +10 copy_file 1831 1834 +3 remove_file 708 707 -1 recursive_action1 420 419 -1 du 468 467 -1 scan_and_display_dirs_recur 675 672 -3 concat_subpath_file 39 - -39 ------------------------------------------------------------------------------ (add/remove: 5/1 grow/shrink: 2/4 up/down: 300/-45) Total: 255 bytes Cachegrind tests (-original, +improved): -------------------------------------------------------------------------------- Ir I1mr ILmr Dr D1mr DLmr Dw D1mw DLmw -------------------------------------------------------------------------------- cg_diff_cp:-1,811,369 (100.0%) 1,544 (100.0%) 1,514 (100.0%) 379,597 (100.0%) 3,151 (100.0%) 2,183 (100.0%) 249,874 (100.0%) 1,218 (100.0%) 1,160 (100.0%) PROGRAM TOTALS cg_diff_cp:+1,310,239 (100.0%) 1,550 (100.0%) 1,519 (100.0%) 290,298 (100.0%) 3,152 (100.0%) 2,183 (100.0%) 184,883 (100.0%) 1,218 (100.0%) 1,160 (100.0%) PROGRAM TOTALS cg_diff_du:-11,080,026 (100.0%) 1,692 (100.0%) 1,627 (100.0%) 2,345,969 (100.0%) 5,603 (100.0%) 2,524 (100.0%) 1,537,107 (100.0%) 1,838 (100.0%) 1,342 (100.0%) PROGRAM TOTALS cg_diff_du:+4,522,979 (100.0%) 1,635 (100.0%) 1,592 (100.0%) 1,189,256 (100.0%) 4,911 (100.0%) 2,513 (100.0%) 784,551 (100.0%) 1,636 (100.0%) 1,287 (100.0%) PROGRAM TOTALS cg_diff_find:-10,719,682 (100.0%) 1,638 (100.0%) 1,592 (100.0%) 2,360,985 (100.0%) 4,149 (100.0%) 2,634 (100.0%) 1,493,014 (100.0%) 1,096 (100.0%) 836 (100.0%) PROGRAM TOTALS cg_diff_find:+4,212,414 (100.0%) 1,527 (100.0%) 1,498 (100.0%) 1,215,858 (100.0%) 3,748 (100.0%) 2,629 (100.0%) 734,040 (100.0%) 850 (100.0%) 732 (100.0%) PROGRAM TOTALS cg_diff_ls:-17,363,363 (100.0%) 1,984 (100.0%) 1,731 (100.0%) 3,751,223 (100.0%) 33,435 (100.0%) 2,439 (100.0%) 2,805,925 (100.0%) 9,422 (100.0%) 2,713 (100.0%) PROGRAM TOTALS cg_diff_ls:+11,166,139 (100.0%) 1,774 (100.0%) 1,683 (100.0%) 2,666,248 (100.0%) 31,111 (100.0%) 2,671 (100.0%) 2,100,224 (100.0%) 9,007 (100.0%) 2,474 (100.0%) PROGRAM TOTALS cg_diff_rm:-6,176,069 (100.0%) 1,585 (100.0%) 1,537 (100.0%) 1,298,524 (100.0%) 3,536 (100.0%) 2,351 (100.0%) 830,656 (100.0%) 905 (100.0%) 802 (100.0%) PROGRAM TOTALS cg_diff_rm:+2,039,241 (100.0%) 1,459 (100.0%) 1,429 (100.0%) 573,877 (100.0%) 3,361 (100.0%) 2,438 (100.0%) 379,660 (100.0%) 724 (100.0%) 663 (100.0%) PROGRAM TOTALS svlogd: rmoldest(): use get_d_namlen() last_char_is_fast: more robust parameter check concat_path_file_fast: copy null byte instead of adding one later The file name will always end in a null byte, so copy it, saving 18 bytes of code. function old new delta concat_path_file_fast 193 175 -18 ------------------------------------------------------------------------------ (add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-18) Total: -18 bytes Signed-off-by: Jody Bruchon <jody@jodybruchon.com> Signed-off-by: Roberto A. Foglietta <roberto.foglietta@gmail.com> This is the commit message #2: cache performance boost for recursion, cleanup Comments removal related to functions changed, good for patch inspection by the patch's author but not for production. Hence janitoring the patch. Signed-off-by: Roberto A. Foglietta <roberto.foglietta@gmail.com> This is the commit message #3: cache performance boost for recursion, xmalloc Signed-off-by: Roberto A. Foglietta <roberto.foglietta@gmail.com>
diff --git a/coreutils/du.c b/coreutils/du.c
@@ -200,7 +200,7 @@ static unsigned long long du(const char *filename)
 		}
 
 		while ((entry = readdir(dir))) {
-			newfile = concat_subpath_file(filename, entry->d_name);
+			newfile = concat_subpath_file_fast(filename, entry);
 			if (newfile == NULL)
 				continue;
 			++G.du_depth;
diff --git a/coreutils/ls.c b/coreutils/ls.c
@@ -1025,7 +1025,7 @@ static struct dnode **scan_one_dir(const char *path, unsigned *nfiles_p)
 				continue; /* if only -A, skip . and .. but show other dotfiles */
 			}
 		}
-		fullname = concat_path_file(path, entry->d_name);
+		fullname = concat_path_file_fast(path, entry);
 		cur = my_stat(fullname, bb_basename(fullname), 0);
 		if (!cur) {
 			free(fullname);
diff --git a/include/libbb.h b/include/libbb.h
@@ -584,6 +584,7 @@ char *bb_get_last_path_component_nostrip(const char *path) FAST_FUNC;
 const char *bb_basename(const char *name) FAST_FUNC;
 /* NB: can violate const-ness (similarly to strchr) */
 char *last_char_is(const char *s, int c) FAST_FUNC;
+char *last_char_is_fast(const char *s, int c, int len) FAST_FUNC;
 const char* endofname(const char *name) FAST_FUNC;
 char *is_prefixed_with(const char *string, const char *key) FAST_FUNC;
 char *is_suffixed_with(const char *string, const char *key) FAST_FUNC;
@@ -1832,9 +1833,12 @@ void config_close(parser_t *parser) FAST_FUNC;
  * If path is NULL, it is assumed to be "/".
  * filename should not be NULL. */
 char *concat_path_file(const char *path, const char *filename) FAST_FUNC;
+char *concat_path_file_fast(const char *path, const struct dirent *dirp) FAST_FUNC;
 /* Returns NULL on . and .. */
 char *concat_subpath_file(const char *path, const char *filename) FAST_FUNC;
+char *concat_subpath_file_fast(const char *path, const struct dirent *dirp) FAST_FUNC;
 
+size_t get_d_namlen(const struct dirent * const dirent) FAST_FUNC;
 
 int bb_make_directory(char *path, long mode, int flags) FAST_FUNC;
 
diff --git a/libbb/Kbuild.src b/libbb/Kbuild.src
@@ -40,6 +40,7 @@ lib-y += find_pid_by_name.o
 lib-y += find_root_device.o
 lib-y += full_write.o
 lib-y += get_console.o
+lib-y += get_d_namlen.o
 lib-y += get_last_path_component.o
 lib-y += get_line_from_file.o
 lib-y += getpty.o
diff --git a/libbb/concat_path_file.c b/libbb/concat_path_file.c
@@ -59,6 +59,35 @@ char* FAST_FUNC concat_path_file(const char *path, const char *filename)
 #endif
 }
 
+char* FAST_FUNC concat_path_file_fast(const char *path, const struct dirent *dirp)
+{
+	const char *filename = dirp->d_name;
+	char *buf;
+	int lc_slash = 0;
+	int name_offset, end_offset;
+	int pathlen, namelen;
+
+	if (!path) {
+		path = "";
+		pathlen = 0;
+	} else {
+		pathlen = strlen(path);
+		if (last_char_is_fast(path, '/', pathlen) == NULL) lc_slash = 1;
+	}
+	namelen = get_d_namlen(dirp);
+	while (*filename == '/') {
+		filename++;
+		namelen--;
+	}
+	name_offset = pathlen + lc_slash;
+	end_offset = name_offset + namelen;
+	buf = xmalloc(end_offset + 1);
+	memcpy(buf, path, pathlen);
+	if (lc_slash == 1) *(buf + pathlen) = '/';
+		memcpy((buf + name_offset), filename, namelen + 1);
+	return buf;
+}
+
 /* If second component comes from struct dirent,
  * it's possible to eliminate one strlen() by using name length
  * provided by kernel in struct dirent. See below.
diff --git a/libbb/concat_subpath_file.c b/libbb/concat_subpath_file.c
@@ -20,3 +20,11 @@ char* FAST_FUNC concat_subpath_file(const char *path, const char *f)
 		return NULL;
 	return concat_path_file(path, f);
 }
+
+
+char* FAST_FUNC concat_subpath_file_fast(const char *path, const struct dirent *dirp)
+{
+	if (dirp->d_name && DOT_OR_DOTDOT(dirp->d_name))
+		return NULL;
+	return concat_path_file_fast(path, dirp);
+}
diff --git a/libbb/copy_file.c b/libbb/copy_file.c
@@ -197,7 +197,7 @@ int FAST_FUNC copy_file(const char *source, const char *dest, int flags)
 		while ((d = readdir(dp)) != NULL) {
 			char *new_source, *new_dest;
 
-			new_source = concat_subpath_file(source, d->d_name);
+			new_source = concat_subpath_file_fast(source, d);
 			if (new_source == NULL)
 				continue;
 			new_dest = concat_path_file(dest, d->d_name);
diff --git a/libbb/get_d_namlen.c b/libbb/get_d_namlen.c
@@ -0,0 +1,29 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * Fast acquisition of d_namlen
+ *
+ * Copyright (C) 2024 by Jody Bruchon <jody@jodybruchon.com>
+ * Copied from libjodycode for use with BusyBox
+ *
+ * Licensed under GPLv2 or later, see file LICENSE in this source tree.
+ */
+
+#include "libbb.h"
+
+/* Extract d_namlen from struct dirent */
+size_t get_d_namlen(const struct dirent * const dirent)
+{
+#ifdef _DIRENT_HAVE_D_NAMLEN
+	return dirent->d_namlen;
+#elif defined _DIRENT_HAVE_D_RECLEN
+	const size_t base = (sizeof(struct dirent) - sizeof(((struct dirent *)0)->d_name)) - offsetof(struct dirent, d_name) - 1;
+	size_t skip;
+
+	skip = dirent->d_reclen - (sizeof(struct dirent) - sizeof(((struct dirent *)0)->d_name));
+	if (skip > 0) skip -= base;
+	return skip + strlen(dirent->d_name + skip);
+#else
+	return strlen(dirent->d_name);
+#endif
+	return 0;
+}
diff --git a/libbb/last_char_is.c b/libbb/last_char_is.c
@@ -17,3 +17,13 @@ char* FAST_FUNC last_char_is(const char *s, int c)
 		s++;
 	return (*s == (char)c) ? (char *) s : NULL;
 }
+
+
+/* Same as last_char_is() but uses a known length to skip the loop */
+char* FAST_FUNC last_char_is_fast(const char *s, int c, int len)
+{
+	if (len < 1)
+		return NULL;
+	s += len - 1;
+	return (*s == (char)c) ? (char *) s : NULL;
+}
diff --git a/libbb/lineedit.c b/libbb/lineedit.c
@@ -921,7 +921,7 @@ static NOINLINE unsigned complete_cmd_dir_file(const char *command, int type)
 			if (strncmp(basecmd, name_found, baselen) != 0)
 				continue; /* no */
 
-			found = concat_path_file(lpath, name_found);
+			found = concat_path_file_fast(lpath, next);
 			/* NB: stat() first so that we see is it a directory;
 			 * but if that fails, use lstat() so that
 			 * we still match dangling links */
diff --git a/libbb/recursive_action.c b/libbb/recursive_action.c
@@ -10,6 +10,7 @@
 
 #undef DEBUG_RECURS_ACTION
 
+
 /*
  * Walk down all the directories under the specified
  * location, and do something (something specified
@@ -126,7 +127,7 @@ static int recursive_action1(recursive_state_t *state, const char *fileName)
 		char *nextFile;
 		int s;
 
-		nextFile = concat_subpath_file(fileName, next->d_name);
+		nextFile = concat_subpath_file_fast(fileName, next);
 		if (nextFile == NULL)
 			continue;
 
diff --git a/libbb/remove_file.c b/libbb/remove_file.c
@@ -53,7 +53,7 @@ int FAST_FUNC remove_file(const char *path, int flags)
 		while ((d = readdir(dp)) != NULL) {
 			char *new_path;
 
-			new_path = concat_subpath_file(path, d->d_name);
+			new_path = concat_subpath_file_fast(path, d);
 			if (new_path == NULL)
 				continue;
 			if (remove_file(new_path, flags) < 0)
diff --git a/runit/svlogd.c b/runit/svlogd.c
@@ -517,7 +517,7 @@ static void rmoldest(struct logdir *ld)
 		pause2cannot("open directory, want rotate", ld->name);
 	errno = 0;
 	while ((f = readdir(d))) {
-		if ((f->d_name[0] == '@') && (strlen(f->d_name) == 27)) {
+		if ((f->d_name[0] == '@') && (get_d_namlen(f) == 27)) {
 			if (f->d_name[26] == 't') {
 				if (unlink(f->d_name) == -1)
 					warn2("can't unlink processor leftover", f->d_name);

Original file line number	Diff line number	Diff line change
`@@ -200,7 +200,7 @@ static unsigned long long du(const char *filename)`
`200`	`200`	`}`
`201`	`201`
`202`	`202`	`while ((entry = readdir(dir))) {`
`203`		`- newfile = concat_subpath_file(filename, entry->d_name);`
	`203`	`+ newfile = concat_subpath_file_fast(filename, entry);`
`204`	`204`	`if (newfile == NULL)`
`205`	`205`	`continue;`
`206`	`206`	`++G.du_depth;`
Original file line number	Diff line number	Diff line change
`@@ -1025,7 +1025,7 @@ static struct dnode *scan_one_dir(const char path, unsigned *nfiles_p)`
`1025`	`1025`	`continue; /* if only -A, skip . and .. but show other dotfiles */`
`1026`	`1026`	`}`
`1027`	`1027`	`}`
`1028`		`- fullname = concat_path_file(path, entry->d_name);`
	`1028`	`+ fullname = concat_path_file_fast(path, entry);`
`1029`	`1029`	`cur = my_stat(fullname, bb_basename(fullname), 0);`
`1030`	`1030`	`if (!cur) {`
`1031`	`1031`	`free(fullname);`