[Crash-utility] [PATCH v4 1/4] Improve the performance of symbol searching for kernel modules
HAGIO KAZUHITO(萩尾 一仁)
k-hagio-ab at nec.com
Tue Oct 5 08:51:08 UTC 2021
Hi Tao,
Found another issue.
The first symbol of duplicated ones will not be shown by sym command
after mod -s.
# crash -s
crash> sym cleanup_module | head -n 1
ffffffffc02527ff (t) cleanup_module [fuse]
crash> mod -s fuse
MODULE NAME BASE SIZE OBJECT FILE
ffffffffc025eac0 fuse ffffffffc023f000 151552 /usr/lib/debug/lib/modules/4.18.0-305.el8.x86_64/kernel/fs/fuse/fuse.ko.debug
crash> sym cleanup_module | grep fuse
It looks like symbol_search() has to return the lowest address symbol and
symbol_search_next() returns the next lowest symbol, so removing/installing
module symbols from/to the hash table breaks this.
The patch will need sorted installation or other solution.
Also, I've not looked at this enough, but kallsyms_module_symbol() changes
spx->cnt from lm->mod_ext_symtable. Is there no interference with the
patch?
Thanks,
Kazu
-----Original Message-----
> Currently the sequence for symbol_search to search a symbol is: 1) kernel
> symname hash table, 2) iterate all kernel symbols, 3) iterate all kernel
> modules and their symbols. In the worst case, if a non-exist symbol been
> searched, all 3 stages will be went through. The time consuming status for
> each stage is like:
>
> stage 1 stage 2 stage 3
> 0.007000(ms) 0.593000(ms) 2.421000(ms)
>
> stage 3 takes too much time when comparing to stage 1. This patch introduces
> a symname hash table for kernel modules, to improve the performance of symbol
> searching.
>
> Functions symbol_search and symbol_exists are fundamental and widely used by
> other crash functions, thus the benefit of performance improvement can
> get accumulated. For example, "ps -m" and "irq" commands, which call
> the functions many times, will become faster with the patch.
>
> Signed-off-by: Tao Liu <ltao at redhat.com>
> Reviewed-by: Philipp Rudo <prudo at redhat.com>
> ---
> defs.h | 1 +
> kernel.c | 1 +
> symbols.c | 176 ++++++++++++++++++++++++++++--------------------------
> 3 files changed, 92 insertions(+), 86 deletions(-)
>
> diff --git a/defs.h b/defs.h
> index eb1c71b..c10ebff 100644
> --- a/defs.h
> +++ b/defs.h
> @@ -2751,6 +2751,7 @@ struct symbol_table_data {
> double val_hash_searches;
> double val_hash_iterations;
> struct syment *symname_hash[SYMNAME_HASH];
> + struct syment *mod_symname_hash[SYMNAME_HASH];
> struct symbol_namespace kernel_namespace;
> struct syment *ext_module_symtable;
> struct syment *ext_module_symend;
> diff --git a/kernel.c b/kernel.c
> index b2c8a0c..307eeee 100644
> --- a/kernel.c
> +++ b/kernel.c
> @@ -4663,6 +4663,7 @@ reinit_modules(void)
> kt->mods_installed = 0;
> clear_text_value_cache();
>
> + memset(st->mod_symname_hash, 0, sizeof(st->mod_symname_hash));
> module_init();
> }
>
> diff --git a/symbols.c b/symbols.c
> index bf6d94d..7ab47f2 100644
> --- a/symbols.c
> +++ b/symbols.c
> @@ -64,8 +64,10 @@ static int namespace_ctl(int, struct symbol_namespace *, void *, void *);
> static void symval_hash_init(void);
> static struct syment *symval_hash_search(ulong);
> static void symname_hash_init(void);
> -static void symname_hash_install(struct syment *);
> -static struct syment *symname_hash_search(char *);
> +static void symname_hash_install(struct syment *[], struct syment *);
> +static void symname_hash_remove(struct syment *[], struct syment *);
> +static struct syment *symname_hash_search(struct syment *[], char *,
> + int (*)(struct syment *, char *));
> static void gnu_qsort(bfd *, void *, long, unsigned int, asymbol *, asymbol *);
> static int check_gnu_debuglink(bfd *);
> static int separate_debug_file_exists(const char *, unsigned long, int *);
> @@ -1119,7 +1121,7 @@ symname_hash_init(void)
> struct syment *sp;
>
> for (sp = st->symtable; sp < st->symend; sp++)
> - symname_hash_install(sp);
> + symname_hash_install(st->symname_hash, sp);
>
> if ((sp = symbol_search("__per_cpu_start")))
> st->__per_cpu_start = sp->value;
> @@ -1127,21 +1129,42 @@ symname_hash_init(void)
> st->__per_cpu_end = sp->value;
> }
>
> +static void
> +mod_symtable_hash_install_range(struct syment *from, struct syment *to)
> +{
> + struct syment *sp;
> +
> + for (sp = from; sp <= to; sp++)
> + symname_hash_install(st->mod_symname_hash, sp);
> +}
> +
> +static void
> +mod_symtable_hash_remove_range(struct syment *from, struct syment *to)
> +{
> + struct syment *sp;
> +
> + for (sp = from; sp <= to; sp++)
> + symname_hash_remove(st->mod_symname_hash, sp);
> +}
> +
> /*
> * Install a single static kernel symbol into the symname_hash.
> */
> static void
> -symname_hash_install(struct syment *spn)
> +symname_hash_install(struct syment *table[], struct syment *spn)
> {
> struct syment *sp;
> int index;
>
> + if (!spn)
> + return;
> +
> index = SYMNAME_HASH_INDEX(spn->name);
> spn->cnt = 1;
>
> - if ((sp = st->symname_hash[index]) == NULL)
> - st->symname_hash[index] = spn;
> - else {
> + if ((sp = table[index]) == NULL) {
> + table[index] = spn;
> + } else {
> while (sp) {
> if (STREQ(sp->name, spn->name)) {
> sp->cnt++;
> @@ -1157,17 +1180,47 @@ symname_hash_install(struct syment *spn)
> }
> }
>
> +static void
> +symname_hash_remove(struct syment *table[], struct syment *spn)
> +{
> + struct syment *sp;
> + int index;
> +
> + if (!spn)
> + return;
> +
> + index = SYMNAME_HASH_INDEX(spn->name);
> +
> + if (table[index] == spn)
> + table[index] = spn->name_hash_next;
> +
> + for (sp = table[index]; sp; sp = sp->name_hash_next) {
> + if (STREQ(sp->name, spn->name))
> + sp->cnt--;
> + if (sp->name_hash_next == spn)
> + sp->name_hash_next = spn->name_hash_next;
> + }
> +}
> +
> /*
> * Static kernel symbol value search
> */
> static struct syment *
> -symname_hash_search(char *name)
> +symname_hash_search(struct syment *table[], char *name,
> + int (*skip_condition)(struct syment *, char *))
> {
> struct syment *sp;
> + int index;
>
> - sp = st->symname_hash[SYMNAME_HASH_INDEX(name)];
> + index = SYMNAME_HASH_INDEX(name);
> + sp = table[index];
>
> while (sp) {
> + if (skip_condition && skip_condition(sp, name)) {
> + sp = sp->name_hash_next;
> + continue;
> + }
> +
> if (STREQ(sp->name, name))
> return sp;
> sp = sp->name_hash_next;
> @@ -1595,6 +1648,7 @@ store_module_symbols_v1(ulong total, int mods_installed)
> lm->mod_symend = sp;
> }
> }
> + mod_symtable_hash_install_range(lm->mod_symtable, lm->mod_symend);
> }
>
> st->flags |= MODULE_SYMS;
> @@ -2075,6 +2129,8 @@ store_module_symbols_v2(ulong total, int mods_installed)
> lm->mod_init_symend = sp;
> }
> }
> + mod_symtable_hash_install_range(lm->mod_symtable, lm->mod_symend);
> + mod_symtable_hash_install_range(lm->mod_init_symtable, lm->mod_init_symend);
> }
>
> st->flags |= MODULE_SYMS;
> @@ -4482,6 +4538,17 @@ symbol_query(char *s, char *print_pad, struct syment **spp)
> return(cnt);
> }
>
> +static int
> +skip_symbols(struct syment *sp, char *s)
> +{
> + int pseudos, skip = 0;
> +
> + pseudos = (strstr(s, "_MODULE_START_") || strstr(s, "_MODULE_END_") ||
> + strstr(s, "_MODULE_INIT_START_") || strstr(s, "_MODULE_INIT_END_"));
> + if (!pseudos && MODULE_PSEUDO_SYMBOL(sp))
> + skip = 1;
> + return skip;
> +}
>
> /*
> * Return the syment of a symbol.
> @@ -4489,58 +4556,16 @@ symbol_query(char *s, char *print_pad, struct syment **spp)
> struct syment *
> symbol_search(char *s)
> {
> - int i;
> - struct syment *sp_hashed, *sp, *sp_end;
> - struct load_module *lm;
> - int pseudos, search_init;
> + struct syment *sp_hashed, *sp;
>
> - sp_hashed = symname_hash_search(s);
> + sp_hashed = symname_hash_search(st->symname_hash, s, NULL);
>
> for (sp = sp_hashed ? sp_hashed : st->symtable; sp < st->symend; sp++) {
> if (STREQ(s, sp->name))
> return(sp);
> }
>
> - pseudos = (strstr(s, "_MODULE_START_") || strstr(s, "_MODULE_END_"));
> - search_init = FALSE;
> -
> - for (i = 0; i < st->mods_installed; i++) {
> - lm = &st->load_modules[i];
> - if (lm->mod_flags & MOD_INIT)
> - search_init = TRUE;
> - sp = lm->mod_symtable;
> - sp_end = lm->mod_symend;
> -
> - for ( ; sp <= sp_end; sp++) {
> - if (!pseudos && MODULE_PSEUDO_SYMBOL(sp))
> - continue;
> - if (STREQ(s, sp->name))
> - return(sp);
> - }
> - }
> -
> - if (!search_init)
> - return((struct syment *)NULL);
> -
> - pseudos = (strstr(s, "_MODULE_INIT_START_") || strstr(s, "_MODULE_INIT_END_"));
> -
> - for (i = 0; i < st->mods_installed; i++) {
> - lm = &st->load_modules[i];
> - if (!lm->mod_init_symtable)
> - continue;
> - sp = lm->mod_init_symtable;
> - sp_end = lm->mod_init_symend;
> -
> - for ( ; sp < sp_end; sp++) {
> - if (!pseudos && MODULE_PSEUDO_SYMBOL(sp))
> - continue;
> -
> - if (STREQ(s, sp->name))
> - return(sp);
> - }
> - }
> -
> - return((struct syment *)NULL);
> + return symname_hash_search(st->mod_symname_hash, s, skip_symbols);
> }
>
> /*
> @@ -5432,33 +5457,11 @@ value_symbol(ulong value)
> int
> symbol_exists(char *symbol)
> {
> - int i;
> - struct syment *sp, *sp_end;
> - struct load_module *lm;
> -
> - if ((sp = symname_hash_search(symbol)))
> + if (symname_hash_search(st->symname_hash, symbol, NULL))
> return TRUE;
>
> - for (i = 0; i < st->mods_installed; i++) {
> - lm = &st->load_modules[i];
> - sp = lm->mod_symtable;
> - sp_end = lm->mod_symend;
> -
> - for ( ; sp < sp_end; sp++) {
> - if (STREQ(symbol, sp->name))
> - return(TRUE);
> - }
> -
> - if (lm->mod_init_symtable) {
> - sp = lm->mod_init_symtable;
> - sp_end = lm->mod_init_symend;
> -
> - for ( ; sp < sp_end; sp++) {
> - if (STREQ(symbol, sp->name))
> - return(TRUE);
> - }
> - }
> - }
> + if (symname_hash_search(st->mod_symname_hash, symbol, NULL))
> + return TRUE;
>
> return(FALSE);
> }
> @@ -5513,12 +5516,7 @@ per_cpu_symbol_search(char *symbol)
> int
> kernel_symbol_exists(char *symbol)
> {
> - struct syment *sp;
> -
> - if ((sp = symname_hash_search(symbol)))
> - return TRUE;
> - else
> - return FALSE;
> + return !!(symname_hash_search(st->symname_hash, symbol, NULL));
> }
>
> /*
> @@ -5527,7 +5525,7 @@ kernel_symbol_exists(char *symbol)
> struct syment *
> kernel_symbol_search(char *symbol)
> {
> - return symname_hash_search(symbol);
> + return symname_hash_search(st->symname_hash, symbol, NULL);
> }
>
> /*
> @@ -12464,8 +12462,10 @@ store_load_module_symbols(bfd *bfd, int dynamic, void *minisyms,
> error(INFO, "%s: last symbol: %s is not _MODULE_END_%s?\n",
> lm->mod_name, lm->mod_load_symend->name, lm->mod_name);
>
> + mod_symtable_hash_remove_range(lm->mod_symtable, lm->mod_symend);
> lm->mod_symtable = lm->mod_load_symtable;
> lm->mod_symend = lm->mod_load_symend;
> + mod_symtable_hash_install_range(lm->mod_symtable, lm->mod_symend);
>
> lm->mod_flags &= ~MOD_EXT_SYMS;
> lm->mod_flags |= MOD_LOAD_SYMS;
> @@ -12495,6 +12495,7 @@ delete_load_module(ulong base_addr)
> req->name = lm->mod_namelist;
> gdb_interface(req);
> }
> + mod_symtable_hash_remove_range(lm->mod_symtable, lm->mod_symend);
> if (lm->mod_load_symtable) {
> free(lm->mod_load_symtable);
> namespace_ctl(NAMESPACE_FREE,
> @@ -12504,6 +12505,7 @@ delete_load_module(ulong base_addr)
> unlink_module(lm);
> lm->mod_symtable = lm->mod_ext_symtable;
> lm->mod_symend = lm->mod_ext_symend;
> + mod_symtable_hash_install_range(lm->mod_symtable, lm->mod_symend);
> lm->mod_flags &= ~(MOD_LOAD_SYMS|MOD_REMOTE|MOD_NOPATCH);
> lm->mod_flags |= MOD_EXT_SYMS;
> lm->mod_load_symtable = NULL;
> @@ -12532,6 +12534,7 @@ delete_load_module(ulong base_addr)
> req->name = lm->mod_namelist;
> gdb_interface(req);
> }
> + mod_symtable_hash_remove_range(lm->mod_symtable, lm->mod_symend);
> if (lm->mod_load_symtable) {
> free(lm->mod_load_symtable);
> namespace_ctl(NAMESPACE_FREE,
> @@ -12541,6 +12544,7 @@ delete_load_module(ulong base_addr)
> unlink_module(lm);
> lm->mod_symtable = lm->mod_ext_symtable;
> lm->mod_symend = lm->mod_ext_symend;
> + mod_symtable_hash_install_range(lm->mod_symtable, lm->mod_symend);
> lm->mod_flags &= ~(MOD_LOAD_SYMS|MOD_REMOTE|MOD_NOPATCH);
> lm->mod_flags |= MOD_EXT_SYMS;
> lm->mod_load_symtable = NULL;
> --
> 2.29.2
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