[PATCH] reduce top(1) CPU usage by an order of magnitude

[PATCH] reduce top(1) CPU usage by an order of magnitude

[Denis Vlasenko]

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Patch is not mine, Paulo Marques <pmarques@grupopie.com>
wrote it.

I tested in on 2.6.9-rc2. top(1) CPU usage went from ~40% to ~4%
(yes, test box is a rather old piece of junk).

The patch applies cleanly to 2.6.9.
--
vda

[-- Attachment #2: kallsyms.diff --]
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diff -urpN old/kernel/kallsyms.c new/kernel/kallsyms.c
--- old/kernel/kallsyms.c	Sat Aug 14 13:56:23 2004
+++ new/kernel/kallsyms.c	Thu Sep 16 15:52:56 2004
@@ -4,7 +4,12 @@
  * Rewritten and vastly simplified by Rusty Russell for in-kernel
  * module loader:
  *   Copyright 2002 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation
- * Stem compression by Andi Kleen.
+ *
+ * ChangeLog:
+ *
+ * (25/Aug/2004) Paulo Marques <pmarques@grupopie.com>
+ *      Changed the compression method from stem compression to "table lookup"
+ *      compression (see scripts/kallsyms.c for a more complete description)
  */
 #include <linux/kallsyms.h>
 #include <linux/module.h>
@@ -17,7 +22,12 @@
 /* These will be re-linked against their real values during the second link stage */
 extern unsigned long kallsyms_addresses[] __attribute__((weak));
 extern unsigned long kallsyms_num_syms __attribute__((weak));
-extern char kallsyms_names[] __attribute__((weak));
+extern u8 kallsyms_names[] __attribute__((weak));
+
+extern u8 kallsyms_token_table[] __attribute__((weak));
+extern u16 kallsyms_token_index[] __attribute__((weak));
+
+extern unsigned long kallsyms_markers[] __attribute__((weak));
 
 /* Defined by the linker script. */
 extern char _stext[], _etext[], _sinittext[], _einittext[];
@@ -37,21 +47,88 @@ static inline int is_kernel_text(unsigne
 	return 0;
 }
 
+/* expand a compressed symbol data into the resulting uncompressed string,
+   given the offset to where the symbol is in the compressed stream */
+static unsigned int kallsyms_expand_symbol(unsigned int off, char *result)
+{
+	int len, skipped_first = 0;
+	u8 *tptr, *data;
+
+	/* get the compressed symbol length from the first symbol byte */
+	data = &kallsyms_names[off];
+	len = *data;
+	data++;
+
+	/* update the offset to return the offset for the next symbol on
+	 * the compressed stream */
+	off += len + 1;
+
+	/* for every byte on the compressed symbol data, copy the table
+	   entry for that byte */
+	while(len) {
+		tptr = &kallsyms_token_table[ kallsyms_token_index[*data] ];
+		data++;
+		len--;
+
+		while (*tptr) {
+			if(skipped_first) {
+				*result = *tptr;
+				result++;
+			} else
+				skipped_first = 1;
+			tptr++;
+		}
+	}
+
+	*result = '\0';
+
+	/* return to offset to the next symbol */
+	return off;
+}
+
+/* get symbol type information. This is encoded as a single char at the
+ * begining of the symbol name */
+static char kallsyms_get_symbol_type(unsigned int off)
+{
+	/* get just the first code, look it up in the token table, and return the
+	 * first char from this token */
+	return kallsyms_token_table[ kallsyms_token_index[ kallsyms_names[off+1] ] ];
+}
+
+
+/* find the offset on the compressed stream given and index in the
+ * kallsyms array */
+static unsigned int get_symbol_offset(unsigned long pos)
+{
+	u8 *name;
+	int i;
+
+	/* use the closest marker we have. We have markers every 256 positions,
+	 * so that should be close enough */
+	name = &kallsyms_names[ kallsyms_markers[pos>>8] ];
+
+	/* sequentially scan all the symbols up to the point we're searching for.
+	 * Every symbol is stored in a [<len>][<len> bytes of data] format, so we
+	 * just need to add the len to the current pointer for every symbol we
+	 * wish to skip */
+	for(i = 0; i < (pos&0xFF); i++)
+		name = name + (*name) + 1;
+
+	return name - kallsyms_names;
+}
+
 /* Lookup the address for this symbol. Returns 0 if not found. */
 unsigned long kallsyms_lookup_name(const char *name)
 {
 	char namebuf[KSYM_NAME_LEN+1];
 	unsigned long i;
-	char *knames;
+	unsigned int off;
 
-	for (i = 0, knames = kallsyms_names; i < kallsyms_num_syms; i++) {
-		unsigned prefix = *knames++;
+	for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
+		off = kallsyms_expand_symbol(off, namebuf);
 
-		strlcpy(namebuf + prefix, knames, KSYM_NAME_LEN - prefix);
 		if (strcmp(namebuf, name) == 0)
 			return kallsyms_addresses[i];
-
-		knames += strlen(knames) + 1;
 	}
 	return module_kallsyms_lookup_name(name);
 }
@@ -62,7 +139,7 @@ const char *kallsyms_lookup(unsigned lon
 			    unsigned long *offset,
 			    char **modname, char *namebuf)
 {
-	unsigned long i, best = 0;
+	unsigned long i, low, high, mid;
 
 	/* This kernel should never had been booted. */
 	BUG_ON(!kallsyms_addresses);
@@ -71,40 +148,45 @@ const char *kallsyms_lookup(unsigned lon
 	namebuf[0] = 0;
 
 	if (is_kernel_text(addr) || is_kernel_inittext(addr)) {
-		unsigned long symbol_end;
-		char *name = kallsyms_names;
+		unsigned long symbol_end=0;
 
-		/* They're sorted, we could be clever here, but who cares? */
-		for (i = 0; i < kallsyms_num_syms; i++) {
-			if (kallsyms_addresses[i] > kallsyms_addresses[best] &&
-			    kallsyms_addresses[i] <= addr)
-				best = i;
+		/* do a binary search on the sorted kallsyms_addresses array */
+		low = 0;
+		high = kallsyms_num_syms;
+
+		while (high-low > 1) {
+			mid = (low + high) / 2;
+			if (kallsyms_addresses[mid] <= addr) low = mid;
+			else high = mid;
 		}
 
-		/* Grab name */
-		for (i = 0; i <= best; i++) { 
-			unsigned prefix = *name++;
-			strncpy(namebuf + prefix, name, KSYM_NAME_LEN - prefix);
-			name += strlen(name) + 1;
-		}
+		/* search for the first aliased symbol. Aliased symbols are
+		   symbols with the same address */
+		while (low && kallsyms_addresses[low - 1] == kallsyms_addresses[low])
+			--low;
 
-		/* At worst, symbol ends at end of section. */
-		if (is_kernel_inittext(addr))
-			symbol_end = (unsigned long)_einittext;
-		else
-			symbol_end = (unsigned long)_etext;
+		/* Grab name */
+		kallsyms_expand_symbol(get_symbol_offset(low), namebuf);
 
 		/* Search for next non-aliased symbol */
-		for (i = best+1; i < kallsyms_num_syms; i++) {
-			if (kallsyms_addresses[i] > kallsyms_addresses[best]) {
+		for (i = low + 1; i < kallsyms_num_syms; i++) {
+			if (kallsyms_addresses[i] > kallsyms_addresses[low]) {
 				symbol_end = kallsyms_addresses[i];
 				break;
 			}
 		}
 
-		*symbolsize = symbol_end - kallsyms_addresses[best];
+		/* if we found no next symbol, we use the end of the section */
+		if (!symbol_end) {
+			if (is_kernel_inittext(addr))
+				symbol_end = (unsigned long)_einittext;
+			else
+				symbol_end = (unsigned long)_etext;
+		}
+
+		*symbolsize = symbol_end - kallsyms_addresses[low];
 		*modname = NULL;
-		*offset = addr - kallsyms_addresses[best];
+		*offset = addr - kallsyms_addresses[low];
 		return namebuf;
 	}
 
@@ -135,7 +217,7 @@ void __print_symbol(const char *fmt, uns
 	printk(fmt, buffer);
 }
 
-/* To avoid O(n^2) iteration, we carry prefix along. */
+/* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
 struct kallsym_iter
 {
 	loff_t pos;
@@ -168,31 +250,23 @@ static int get_ksymbol_mod(struct kallsy
 /* Returns space to next name. */
 static unsigned long get_ksymbol_core(struct kallsym_iter *iter)
 {
-	unsigned stemlen, off = iter->nameoff;
+	unsigned off = iter->nameoff;
 
-	/* First char of each symbol name indicates prefix length
-	   shared with previous name (stem compression). */
-	stemlen = kallsyms_names[off++];
-
-	strlcpy(iter->name+stemlen, kallsyms_names + off,
-		KSYM_NAME_LEN+1-stemlen);
-	off += strlen(kallsyms_names + off) + 1;
 	iter->owner = NULL;
 	iter->value = kallsyms_addresses[iter->pos];
-	if (is_kernel_text(iter->value) || is_kernel_inittext(iter->value))
-		iter->type = 't';
-	else
-		iter->type = 'd';
 
-	upcase_if_global(iter);
+	iter->type = kallsyms_get_symbol_type(off);
+
+	off = kallsyms_expand_symbol(off, iter->name);
+
 	return off - iter->nameoff;
 }
 
-static void reset_iter(struct kallsym_iter *iter)
+static void reset_iter(struct kallsym_iter *iter, loff_t new_pos)
 {
 	iter->name[0] = '\0';
-	iter->nameoff = 0;
-	iter->pos = 0;
+	iter->nameoff = get_symbol_offset(new_pos);
+	iter->pos = new_pos;
 }
 
 /* Returns false if pos at or past end of file. */
@@ -204,16 +278,13 @@ static int update_iter(struct kallsym_it
 		return get_ksymbol_mod(iter);
 	}
 	
-	/* If we're past the desired position, reset to start. */
-	if (pos < iter->pos)
-		reset_iter(iter);
-
-	/* We need to iterate through the previous symbols: can be slow */
-	for (; iter->pos != pos; iter->pos++) {
-		iter->nameoff += get_ksymbol_core(iter);
-		cond_resched();
-	}
-	get_ksymbol_core(iter);
+	/* If we're not on the desired position, reset to new position. */
+	if (pos != iter->pos)
+		reset_iter(iter, pos);
+
+	iter->nameoff += get_ksymbol_core(iter);
+	iter->pos++;
+
 	return 1;
 }
 
@@ -267,14 +338,15 @@ struct seq_operations kallsyms_op = {
 static int kallsyms_open(struct inode *inode, struct file *file)
 {
 	/* We keep iterator in m->private, since normal case is to
-	 * s_start from where we left off, so we avoid O(N^2). */
+	 * s_start from where we left off, so we avoid doing
+	 * using get_symbol_offset for every symbol */
 	struct kallsym_iter *iter;
 	int ret;
 
 	iter = kmalloc(sizeof(*iter), GFP_KERNEL);
 	if (!iter)
 		return -ENOMEM;
-	reset_iter(iter);
+	reset_iter(iter, 0);
 
 	ret = seq_open(file, &kallsyms_op);
 	if (ret == 0)
@@ -310,3 +382,4 @@ int __init kallsyms_init(void)
 __initcall(kallsyms_init);
 
 EXPORT_SYMBOL(__print_symbol);
+EXPORT_SYMBOL(kallsyms_lookup_name);
diff -urpN old/scripts/kallsyms.c new/scripts/kallsyms.c
--- old/scripts/kallsyms.c	Sat Aug 14 13:56:23 2004
+++ new/scripts/kallsyms.c	Thu Sep 16 15:53:02 2004
@@ -6,6 +6,22 @@
  * of the GNU General Public License, incorporated herein by reference.
  *
  * Usage: nm -n vmlinux | scripts/kallsyms [--all-symbols] > symbols.S
+ *
+ * ChangeLog:
+ *
+ * (25/Aug/2004) Paulo Marques <pmarques@grupopie.com>
+ *      Changed the compression method from stem compression to "table lookup"
+ *      compression
+ *
+ *      Table compression uses all the unused char codes on the symbols and
+ *  maps these to the most used substrings (tokens). For instance, it might
+ *  map char code 0xF7 to represent "write_" and then in every symbol where
+ *  "write_" appears it can be replaced by 0xF7, saving 5 bytes.
+ *      The used codes themselves are also placed in the table so that the
+ *  decompresion can work without "special cases".
+ *      Applied to kernel symbols, this usually produces a compression ratio
+ *  of about 50%.
+ *
  */
 
 #include <stdio.h>
@@ -13,10 +29,39 @@
 #include <string.h>
 #include <ctype.h>
 
+/* maximum token length used. It doesn't pay to increase it a lot, because
+ * very long substrings probably don't repeat themselves too often. */
+#define MAX_TOK_SIZE		11
+#define KSYM_NAME_LEN		127
+
+/* we use only a subset of the complete symbol table to gather the token count,
+ * to speed up compression, at the expense of a little compression ratio */
+#define WORKING_SET		1024
+
+/* first find the best token only on the list of tokens that would profit more
+ * than GOOD_BAD_THRESHOLD. Only if this list is empty go to the "bad" list.
+ * Increasing this value will put less tokens on the "good" list, so the search
+ * is faster. However, if the good list runs out of tokens, we must painfully
+ * search the bad list. */
+#define GOOD_BAD_THRESHOLD	10
+
+/* token hash parameters */
+#define HASH_BITS		18
+#define HASH_TABLE_SIZE		(1 << HASH_BITS)
+#define HASH_MASK		(HASH_TABLE_SIZE - 1)
+#define HASH_BASE_OFFSET	2166136261U
+#define HASH_FOLD(a)		((a)&(HASH_MASK))
+
+/* flags to mark symbols */
+#define SYM_FLAG_VALID		1
+#define SYM_FLAG_SAMPLED	2
+
 struct sym_entry {
 	unsigned long long addr;
 	char type;
-	char *sym;
+	unsigned char flags;
+	unsigned char len;
+	unsigned char *sym;
 };
 
 
@@ -25,6 +70,26 @@ static int size, cnt;
 static unsigned long long _stext, _etext, _sinittext, _einittext;
 static int all_symbols = 0;
 
+struct token {
+	unsigned char data[MAX_TOK_SIZE];
+	unsigned char len;
+	/* profit: the number of bytes that could be saved by inserting this
+	 * token into the table */
+	int profit;
+	struct token *next;	/* next token on the hash list */
+	struct token *right;	/* next token on the good/bad list */
+	struct token *left;    /* previous token on the good/bad list */
+	struct token *smaller; /* token that is less one letter than this one */
+	};
+
+struct token bad_head, good_head;
+struct token *hash_table[HASH_TABLE_SIZE];
+
+/* the table that holds the result of the compression */
+unsigned char best_table[256][MAX_TOK_SIZE+1];
+unsigned char best_table_len[256];
+
+
 static void
 usage(void)
 {
@@ -59,34 +124,53 @@ read_symbol(FILE *in, struct sym_entry *
 	else if (toupper(s->type) == 'A' || toupper(s->type) == 'U')
 		return -1;
 
-	s->sym = strdup(str);
+	/* include the type field in the symbol name, so that it gets
+	 * compressed together */
+	s->len = strlen(str) + 1;
+	s->sym = (char *) malloc(s->len + 1);
+	strcpy(s->sym + 1, str);
+	s->sym[0] = s->type;
+
 	return 0;
 }
 
 static int
 symbol_valid(struct sym_entry *s)
 {
+	/* Symbols which vary between passes.  Passes 1 and 2 must have
+	 * identical symbol lists.  The kallsyms_* symbols below are only added
+	 * after pass 1, they would be included in pass 2 when --all-symbols is
+	 * specified so exclude them to get a stable symbol list.
+	 */
+	static char *special_symbols[] = {
+		"kallsyms_addresses",
+		"kallsyms_num_syms",
+		"kallsyms_names",
+		"kallsyms_markers",
+		"kallsyms_token_table",
+		"kallsyms_token_index",
+
+	/* Exclude linker generated symbols which vary between passes */
+		"_SDA_BASE_",		/* ppc */
+		"_SDA2_BASE_",		/* ppc */
+		NULL };
+	int i;
+
+	/* if --all-symbols is not specified, then symbols outside the text
+	 * and inittext sections are discarded */
 	if (!all_symbols) {
 		if ((s->addr < _stext || s->addr > _etext)
 		    && (s->addr < _sinittext || s->addr > _einittext))
 			return 0;
 	}
 
-	/* Exclude symbols which vary between passes.  Passes 1 and 2 must have
-	 * identical symbol lists.  The kallsyms_* symbols below are only added
-	 * after pass 1, they would be included in pass 2 when --all-symbols is
-	 * specified so exclude them to get a stable symbol list.
-	 */
-	if (strstr(s->sym, "_compiled.") ||
-	    strcmp(s->sym, "kallsyms_addresses") == 0 ||
-	    strcmp(s->sym, "kallsyms_num_syms") == 0 ||
-	    strcmp(s->sym, "kallsyms_names") == 0)
+	/* Exclude symbols which vary between passes. */
+	if (strstr(s->sym + 1, "_compiled."))
 		return 0;
 
-	/* Exclude linker generated symbols which vary between passes */
-	if (strcmp(s->sym, "_SDA_BASE_") == 0 ||	/* ppc */
-	    strcmp(s->sym, "_SDA2_BASE_") == 0)		/* ppc */
-		return 0;
+	for (i = 0; special_symbols[i]; i++)
+		if( strcmp(s->sym + 1, special_symbols[i]) == 0 )
+			return 0;
 
 	return 1;
 }
@@ -108,11 +192,47 @@ read_map(FILE *in)
 	}
 }
 
+static void output_label(char *label)
+{
+	printf(".globl %s\n",label);
+	printf("\tALGN\n");
+	printf("%s:\n",label);
+}
+
+/* uncompress a compressed symbol. When this function is called, the best table
+ * might still be compressed itself, so the function needs to be recursive */
+static int expand_symbol(unsigned char *data, int len, char *result)
+{
+	int c, rlen, total=0;
+
+	while (len) {
+		c = *data;
+		/* if the table holds a single char that is the same as the one
+		 * we are looking for, then end the search */
+		if (best_table[c][0]==c && best_table_len[c]==1) {
+			*result++ = c;
+			total++;
+		} else {
+			/* if not, recurse and expand */
+			rlen = expand_symbol(best_table[c], best_table_len[c], result);
+			total += rlen;
+			result += rlen;
+		}
+		data++;
+		len--;
+	}
+	*result=0;
+
+	return total;
+}
+
 static void
 write_src(void)
 {
-	int i, valid = 0;
-	char *prev;
+	int i, k, off, valid;
+	unsigned int best_idx[256];
+	unsigned int *markers;
+	char buf[KSYM_NAME_LEN+1];
 
 	printf("#include <asm/types.h>\n");
 	printf("#if BITS_PER_LONG == 64\n");
@@ -125,43 +245,399 @@ write_src(void)
 
 	printf(".data\n");
 
-	printf(".globl kallsyms_addresses\n");
-	printf("\tALGN\n");
-	printf("kallsyms_addresses:\n");
+	output_label("kallsyms_addresses");
+	valid = 0;
 	for (i = 0; i < cnt; i++) {
-		if (!symbol_valid(&table[i]))
-			continue;
-
-		printf("\tPTR\t%#llx\n", table[i].addr);
-		valid++;
+		if (table[i].flags & SYM_FLAG_VALID) {
+			printf("\tPTR\t%#llx\n", table[i].addr);
+			valid++;
+		}
 	}
 	printf("\n");
 
-	printf(".globl kallsyms_num_syms\n");
-	printf("\tALGN\n");
-	printf("kallsyms_num_syms:\n");
+	output_label("kallsyms_num_syms");
 	printf("\tPTR\t%d\n", valid);
 	printf("\n");
 
-	printf(".globl kallsyms_names\n");
-	printf("\tALGN\n");
-	printf("kallsyms_names:\n");
-	prev = ""; 
+	/* table of offset markers, that give the offset in the compressed stream
+	 * every 256 symbols */
+	markers = (unsigned int *) malloc(sizeof(unsigned int)*((valid + 255) / 256));
+
+	output_label("kallsyms_names");
+	valid = 0;
+	off = 0;
 	for (i = 0; i < cnt; i++) {
-		int k;
 
-		if (!symbol_valid(&table[i]))
+		if (!table[i].flags & SYM_FLAG_VALID)
 			continue;
 
-		for (k = 0; table[i].sym[k] && table[i].sym[k] == prev[k]; ++k)
-			; 
+		if ((valid & 0xFF) == 0)
+			markers[valid >> 8] = off;
+
+		printf("\t.byte 0x%02x", table[i].len);
+		for (k = 0; k < table[i].len; k++)
+			printf(", 0x%02x", table[i].sym[k]);
+		printf("\n");
 
-		printf("\t.byte 0x%02x\n\t.asciz\t\"%s\"\n", k, table[i].sym + k);
-		prev = table[i].sym;
+		off += table[i].len + 1;
+		valid++;
 	}
 	printf("\n");
+
+	output_label("kallsyms_markers");
+	for (i = 0; i < ((valid + 255) >> 8); i++)
+		printf("\tPTR\t%d\n", markers[i]);
+	printf("\n");
+
+	free(markers);
+
+	output_label("kallsyms_token_table");
+	off = 0;
+	for (i = 0; i < 256; i++) {
+		best_idx[i] = off;
+		expand_symbol(best_table[i],best_table_len[i],buf);
+		printf("\t.asciz\t\"%s\"\n", buf);
+		off += strlen(buf) + 1;
+	}
+	printf("\n");
+
+	output_label("kallsyms_token_index");
+	for (i = 0; i < 256; i++)
+		printf("\t.short\t%d\n", best_idx[i]);
+	printf("\n");
+}
+
+
+/* table lookup compression functions */
+
+static inline unsigned int rehash_token(unsigned int hash, unsigned char data)
+{
+	return ((hash * 16777619) ^ data);
+}
+
+static unsigned int hash_token(unsigned char *data, int len)
+{
+	unsigned int hash=HASH_BASE_OFFSET;
+	int i;
+
+	for (i = 0; i < len; i++)
+		hash = rehash_token(hash, data[i]);
+
+	return HASH_FOLD(hash);
+}
+
+/* find a token given its data and hash value */
+static struct token *find_token_hash(unsigned char *data, int len, unsigned int hash)
+{
+	struct token *ptr;
+
+	ptr = hash_table[hash];
+
+	while (ptr) {
+		if ((ptr->len == len) && (memcmp(ptr->data, data, len) == 0))
+			return ptr;
+		ptr=ptr->next;
+	}
+
+	return NULL;
+}
+
+static inline void insert_token_in_group(struct token *head, struct token *ptr)
+{
+	ptr->right = head->right;
+	ptr->right->left = ptr;
+	head->right = ptr;
+	ptr->left = head;
+}
+
+static inline void remove_token_from_group(struct token *ptr)
+{
+	ptr->left->right = ptr->right;
+	ptr->right->left = ptr->left;
+}
+
+
+/* build the counts for all the tokens that start with "data", and have lenghts
+ * from 2 to "len" */
+static void learn_token(unsigned char *data, int len)
+{
+	struct token *ptr,*last_ptr;
+	int i, newprofit;
+	unsigned int hash = HASH_BASE_OFFSET;
+	unsigned int hashes[MAX_TOK_SIZE + 1];
+
+	if (len > MAX_TOK_SIZE)
+		len = MAX_TOK_SIZE;
+
+	/* calculate and store the hash values for all the sub-tokens */
+	hash = rehash_token(hash, data[0]);
+	for (i = 2; i <= len; i++) {
+		hash = rehash_token(hash, data[i-1]);
+		hashes[i] = HASH_FOLD(hash);
+	}
+
+	last_ptr = NULL;
+	ptr = NULL;
+
+	for (i = len; i >= 2; i--) {
+		hash = hashes[i];
+
+		if (!ptr) ptr = find_token_hash(data, i, hash);
+
+		if (!ptr) {
+			/* create a new token entry */
+			ptr = (struct token *) malloc(sizeof(*ptr));
+
+			memcpy(ptr->data, data, i);
+			ptr->len = i;
+
+			/* when we create an entry, it's profit is 0 because
+			 * we also take into account the size of the token on
+			 * the compressed table. We then subtract GOOD_BAD_THRESHOLD
+			 * so that the test to see if this token belongs to
+			 * the good or bad list, is a comparison to zero */
+			ptr->profit = -GOOD_BAD_THRESHOLD;
+
+			ptr->next = hash_table[hash];
+			hash_table[hash] = ptr;
+
+			insert_token_in_group(&bad_head, ptr);
+
+			ptr->smaller = NULL;
+		} else {
+			newprofit = ptr->profit + (ptr->len - 1);
+			/* check to see if this token needs to be moved to a
+			 * different list */
+			if((ptr->profit < 0) && (newprofit >= 0)) {
+				remove_token_from_group(ptr);
+				insert_token_in_group(&good_head,ptr);
+			}
+			ptr->profit = newprofit;
+		}
+
+		if (last_ptr) last_ptr->smaller = ptr;
+		last_ptr = ptr;
+
+		ptr = ptr->smaller;
+	}
+}
+
+/* decrease the counts for all the tokens that start with "data", and have lenghts
+ * from 2 to "len". This function is much simpler than learn_token because we have
+ * more guarantees (tho tokens exist, the ->smaller pointer is set, etc.)
+ * The two separate functions exist only because of compression performance */
+static void forget_token(unsigned char *data, int len)
+{
+	struct token *ptr;
+	int i, newprofit;
+	unsigned int hash=0;
+
+	if (len > MAX_TOK_SIZE) len = MAX_TOK_SIZE;
+
+	hash = hash_token(data, len);
+	ptr = find_token_hash(data, len, hash);
+
+	for (i = len; i >= 2; i--) {
+
+		newprofit = ptr->profit - (ptr->len - 1);
+		if ((ptr->profit >= 0) && (newprofit < 0)) {
+			remove_token_from_group(ptr);
+			insert_token_in_group(&bad_head, ptr);
+		}
+		ptr->profit=newprofit;
+
+		ptr=ptr->smaller;
+	}
+}
+
+/* count all the possible tokens in a symbol */
+static void learn_symbol(unsigned char *symbol, int len)
+{
+	int i;
+
+	for (i = 0; i < len - 1; i++)
+		learn_token(symbol + i, len - i);
+}
+
+/* decrease the count for all the possible tokens in a symbol */
+static void forget_symbol(unsigned char *symbol, int len)
+{
+	int i;
+
+	for (i = 0; i < len - 1; i++)
+		forget_token(symbol + i, len - i);
+}
+
+/* set all the symbol flags and do the initial token count */
+static void build_initial_tok_table(void)
+{
+	int i, use_it, valid;
+
+	valid = 0;
+	for (i = 0; i < cnt; i++) {
+		table[i].flags = 0;
+		if ( symbol_valid(&table[i]) ) {
+			table[i].flags |= SYM_FLAG_VALID;
+			valid++;
+		}
+	}
+
+	use_it = 0;
+	for (i = 0; i < cnt; i++) {
+
+		/* subsample the available symbols. This method is almost like
+		 * a Bresenham's algorithm to get uniformly distributed samples
+		 * across the symbol table */
+		if (table[i].flags & SYM_FLAG_VALID) {
+
+			use_it += WORKING_SET;
+
+			if (use_it >= valid) {
+				table[i].flags |= SYM_FLAG_SAMPLED;
+				use_it -= valid;
+			}
+		}
+		if (table[i].flags & SYM_FLAG_SAMPLED)
+			learn_symbol(table[i].sym, table[i].len);
+	}
 }
 
+/* replace a given token in all the valid symbols. Use the sampled symbols
+ * to update the counts */
+static void compress_symbols(unsigned char *str, int tlen, int idx)
+{
+	int i, len, learn, size;
+	unsigned char *p;
+
+	for (i = 0; i < cnt; i++) {
+
+		if (!(table[i].flags & SYM_FLAG_VALID)) continue;
+
+		len = table[i].len;
+		learn = 0;
+		p = table[i].sym;
+
+		do {
+			/* find the token on the symbol */
+			p = (unsigned char *) strstr((char *) p, (char *) str);
+			if (!p) break;
+
+			if (!learn) {
+				/* if this symbol was used to count, decrease it */
+				if (table[i].flags & SYM_FLAG_SAMPLED)
+					forget_symbol(table[i].sym, len);
+				learn = 1;
+			}
+
+			*p = idx;
+			size = (len - (p - table[i].sym)) - tlen + 1;
+			memmove(p + 1, p + tlen, size);
+			p++;
+			len -= tlen - 1;
+
+		} while (size >= tlen);
+
+		if(learn) {
+			table[i].len = len;
+			/* if this symbol was used to count, learn it again */
+			if(table[i].flags & SYM_FLAG_SAMPLED)
+				learn_symbol(table[i].sym, len);
+		}
+	}
+}
+
+/* search the token with the maximum profit */
+static struct token *find_best_token(void)
+{
+	struct token *ptr,*best,*head;
+	int bestprofit;
+
+	bestprofit=-10000;
+
+	/* failsafe: if the "good" list is empty search from the "bad" list */
+	if(good_head.right == &good_head) head = &bad_head;
+	else head = &good_head;
+
+	ptr = head->right;
+	best = NULL;
+	while (ptr != head) {
+		if (ptr->profit > bestprofit) {
+			bestprofit = ptr->profit;
+			best = ptr;
+		}
+		ptr = ptr->right;
+	}
+
+	return best;
+}
+
+/* this is the core of the algorithm: calculate the "best" table */
+static void optimize_result(void)
+{
+	struct token *best;
+	int i;
+
+	/* using the '\0' symbol last allows compress_symbols to use standard
+	 * fast string functions */
+	for (i = 255; i >= 0; i--) {
+
+		/* if this table slot is empty (it is not used by an actual
+		 * original char code */
+		if (!best_table_len[i]) {
+
+			/* find the token with the breates profit value */
+			best = find_best_token();
+
+			/* place it in the "best" table */
+			best_table_len[i] = best->len;
+			memcpy(best_table[i], best->data, best_table_len[i]);
+			/* zero terminate the token so that we can use strstr
+			   in compress_symbols */
+			best_table[i][best_table_len[i]]='\0';
+
+			/* replace this token in all the valid symbols */
+			compress_symbols(best_table[i], best_table_len[i], i);
+		}
+	}
+}
+
+/* start by placing the symbols that are actually used on the table */
+static void insert_real_symbols_in_table(void)
+{
+	int i, j, c;
+
+	memset(best_table, 0, sizeof(best_table));
+	memset(best_table_len, 0, sizeof(best_table_len));
+
+	for (i = 0; i < cnt; i++) {
+		if (table[i].flags & SYM_FLAG_VALID) {
+			for (j = 0; j < table[i].len; j++) {
+				c = table[i].sym[j];
+				best_table[c][0]=c;
+				best_table_len[c]=1;
+			}
+		}
+	}
+}
+
+static void optimize_token_table(void)
+{
+	memset(hash_table, 0, sizeof(hash_table));
+
+	good_head.left = &good_head;
+	good_head.right = &good_head;
+
+	bad_head.left = &bad_head;
+	bad_head.right = &bad_head;
+
+	build_initial_tok_table();
+
+	insert_real_symbols_in_table();
+
+	optimize_result();
+}
+
+
 int
 main(int argc, char **argv)
 {
@@ -171,6 +647,7 @@ main(int argc, char **argv)
 		usage();
 
 	read_map(stdin);
+	optimize_token_table();
 	write_src();
 
 	return 0;

Re: [PATCH] reduce top(1) CPU usage by an order of magnitude

[Andi Kleen]

Denis Vlasenko <vda@port.imtp.ilyichevsk.odessa.ua> writes:

> Patch is not mine, Paulo Marques <pmarques@grupopie.com>
> wrote it.

The bug is in your top. It shouldn't read /proc/*/wchan
by default unless the user switches on WCHAN display.
Just disable that and it will be even faster. My top
doesn't read it at all, you probably got some buggy
version.

Also btw we normally let people submit their patches themselves.

-Andi

Re: [PATCH] reduce top(1) CPU usage by an order of magnitude

[Andrew Morton]

Denis Vlasenko <vda@port.imtp.ilyichevsk.odessa.ua> wrote:
>
> Patch is not mine, Paulo Marques <pmarques@grupopie.com>
>  wrote it.
> 
>  I tested in on 2.6.9-rc2. top(1) CPU usage went from ~40% to ~4%
>  (yes, test box is a rather old piece of junk).
> 
>  The patch applies cleanly to 2.6.9.

umm, this patch has been in -mm for six weeks, and in Linus's kernel for
one week.

Re: [PATCH] reduce top(1) CPU usage by an order of magnitude

[Nick Piggin]

Denis Vlasenko wrote:
> Patch is not mine, Paulo Marques <pmarques@grupopie.com>
> wrote it.
> 
> I tested in on 2.6.9-rc2. top(1) CPU usage went from ~40% to ~4%
> (yes, test box is a rather old piece of junk).
> 
> The patch applies cleanly to 2.6.9.

Patch is already merged.

Re: [PATCH] reduce top(1) CPU usage by an order of magnitude

[Denis Vlasenko]

On Monday 25 October 2004 10:35, Andi Kleen wrote:
> Denis Vlasenko <vda@port.imtp.ilyichevsk.odessa.ua> writes:
> 
> > Patch is not mine, Paulo Marques <pmarques@grupopie.com>
> > wrote it.
> 
> The bug is in your top. It shouldn't read /proc/*/wchan
> by default unless the user switches on WCHAN display.
> Just disable that and it will be even faster. My top
> doesn't read it at all, you probably got some buggy
> version.

This is top from procps-2.0.18.
You are right, top may skip reading wchan, I will look into it.
However, if I do request WCHAN, I still want top to be fast.
 
> Also btw we normally let people submit their patches themselves.

I just wanted to prevent this patch from being missed.
--
vda

Re: [PATCH] reduce top(1) CPU usage by an order of magnitude

[Denis Vlasenko]

On Monday 25 October 2004 10:36, Andrew Morton wrote:
> Denis Vlasenko <vda@port.imtp.ilyichevsk.odessa.ua> wrote:
> >
> > Patch is not mine, Paulo Marques <pmarques@grupopie.com>
> >  wrote it.
> > 
> >  I tested in on 2.6.9-rc2. top(1) CPU usage went from ~40% to ~4%
> >  (yes, test box is a rather old piece of junk).
> > 
> >  The patch applies cleanly to 2.6.9.
> 
> umm, this patch has been in -mm for six weeks, and in Linus's kernel for
> one week.

Good.

Sorry for the noise.
--
vda