From 9fdbd3eed2c748d1728aef440264cac2b21c546e Mon Sep 17 00:00:00 2001 From: Zhen Lei Date: Wed, 2 Nov 2022 16:49:14 +0800 Subject: [PATCH] kallsyms: Improve the performance of kallsyms_lookup_name() Currently, to search for a symbol, we need to expand the symbols in 'kallsyms_names' one by one, and then use the expanded string for comparison. It's O(n). If we sort names in ascending order like addresses, we can also use binary search. It's O(log(n)). In order not to change the implementation of "/proc/kallsyms", the table kallsyms_names[] is still stored in a one-to-one correspondence with the address in ascending order. Add array kallsyms_seqs_of_names[], it's indexed by the sequence number of the sorted names, and the corresponding content is the sequence number of the sorted addresses. For example: Assume that the index of NameX in array kallsyms_seqs_of_names[] is 'i', the content of kallsyms_seqs_of_names[i] is 'k', then the corresponding address of NameX is kallsyms_addresses[k]. The offset in kallsyms_names[] is get_symbol_offset(k). Note that the memory usage will increase by (4 * kallsyms_num_syms) bytes, the next two patches will reduce (1 * kallsyms_num_syms) bytes and properly handle the case CONFIG_LTO_CLANG=y. Performance test results: (x86) Before: min=234, max=10364402, avg=5206926 min=267, max=11168517, avg=5207587 After: min=1016, max=90894, avg=7272 min=1014, max=93470, avg=7293 The average lookup performance of kallsyms_lookup_name() improved 715x. Signed-off-by: Zhen Lei Signed-off-by: Luis Chamberlain --- kernel/kallsyms.c | 87 ++++++++++++++++++++++++++++++++++++++++------ scripts/kallsyms.c | 37 ++++++++++++++++++++ 2 files changed, 113 insertions(+), 11 deletions(-) diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c index 17d3a704b..3103629f3 100755 --- a/kernel/kallsyms.c +++ b/kernel/kallsyms.c @@ -49,6 +49,7 @@ extern const char kallsyms_token_table[] __weak; extern const u16 kallsyms_token_index[] __weak; extern const unsigned int kallsyms_markers[] __weak; +extern const unsigned int kallsyms_seqs_of_names[] __weak; /* * Expand a compressed symbol data into the resulting uncompressed string, @@ -181,22 +182,86 @@ static inline char *cleanup_symbol_name(char *s) static inline char *cleanup_symbol_name(char *s) { return NULL; } #endif +static int compare_symbol_name(const char *name, char *namebuf) +{ + int ret; + + ret = strcmp(name, namebuf); + if (!ret) + return ret; + + if (cleanup_symbol_name(namebuf) && !strcmp(name, namebuf)) + return 0; + + return ret; +} + +static int kallsyms_lookup_names(const char *name, + unsigned int *start, + unsigned int *end) +{ + int ret; + int low, mid, high; + unsigned int seq, off; + char namebuf[KSYM_NAME_LEN]; + + low = 0; + high = kallsyms_num_syms - 1; + + while (low <= high) { + mid = low + (high - low) / 2; + seq = kallsyms_seqs_of_names[mid]; + off = get_symbol_offset(seq); + kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf)); + ret = compare_symbol_name(name, namebuf); + if (ret > 0) + low = mid + 1; + else if (ret < 0) + high = mid - 1; + else + break; + } + + if (low > high) + return -ESRCH; + + low = mid; + while (low) { + seq = kallsyms_seqs_of_names[low - 1]; + off = get_symbol_offset(seq); + kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf)); + if (compare_symbol_name(name, namebuf)) + break; + low--; + } + *start = low; + + if (end) { + high = mid; + while (high < kallsyms_num_syms - 1) { + seq = kallsyms_seqs_of_names[high + 1]; + off = get_symbol_offset(seq); + kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf)); + if (compare_symbol_name(name, namebuf)) + break; + high++; + } + *end = high; + } + + return 0; +} + /* Lookup the address for this symbol. Returns 0 if not found. */ unsigned long kallsyms_lookup_name(const char *name) { - char namebuf[KSYM_NAME_LEN]; - unsigned long i; - unsigned int off; + int ret; + unsigned int i; - for (i = 0, off = 0; i < kallsyms_num_syms; i++) { - off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf)); + ret = kallsyms_lookup_names(name, &i, NULL); + if (!ret) + return kallsyms_sym_address(kallsyms_seqs_of_names[i]); - if (strcmp(namebuf, name) == 0) - return kallsyms_sym_address(i); - - if (cleanup_symbol_name(namebuf) && strcmp(namebuf, name) == 0) - return kallsyms_sym_address(i); - } return module_kallsyms_lookup_name(name); } diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c index 54ad86d13..d70aa19c4 100755 --- a/scripts/kallsyms.c +++ b/scripts/kallsyms.c @@ -32,6 +32,7 @@ struct sym_entry { unsigned long long addr; unsigned int len; + unsigned int seq; unsigned int start_pos; unsigned int percpu_absolute; unsigned char sym[]; @@ -384,6 +385,35 @@ static int symbol_absolute(const struct sym_entry *s) return s->percpu_absolute; } +static int compare_names(const void *a, const void *b) +{ + int ret; + char sa_namebuf[KSYM_NAME_LEN]; + char sb_namebuf[KSYM_NAME_LEN]; + const struct sym_entry *sa = *(const struct sym_entry **)a; + const struct sym_entry *sb = *(const struct sym_entry **)b; + + expand_symbol(sa->sym, sa->len, sa_namebuf); + expand_symbol(sb->sym, sb->len, sb_namebuf); + ret = strcmp(&sa_namebuf[1], &sb_namebuf[1]); + if (!ret) { + if (sa->addr > sb->addr) + return 1; + else if (sa->addr < sb->addr) + return -1; + + /* keep old order */ + return (int)(sa->seq - sb->seq); + } + + return ret; +} + +static void sort_symbols_by_name(void) +{ + qsort(table, table_cnt, sizeof(table[0]), compare_names); +} + static void write_src(void) { unsigned int i, k, off; @@ -469,6 +499,7 @@ static void write_src(void) for (i = 0; i < table_cnt; i++) { if ((i & 0xFF) == 0) markers[i >> 8] = off; + table[i]->seq = i; printf("\t.byte 0x%02x", table[i]->len); for (k = 0; k < table[i]->len; k++) @@ -486,6 +517,12 @@ static void write_src(void) free(markers); + sort_symbols_by_name(); + output_label("kallsyms_seqs_of_names"); + for (i = 0; i < table_cnt; i++) + printf("\t.long\t%u\n", table[i]->seq); + printf("\n"); + output_label("kallsyms_token_table"); off = 0; for (i = 0; i < 256; i++) {