[Crash-utility] [PATCH v3 1/4] Improve the performance of symbol searching for kernel modules
Philipp Rudo
prudo at redhat.com
Fri Sep 17 08:59:55 UTC 2021
Hi Tao,
On Tue, 14 Sep 2021 17:01:51 +0800
Tao Liu <ltao at redhat.com> wrote:
> 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>
> ---
> defs.h | 1 +
> kernel.c | 1 +
> symbols.c | 167 +++++++++++++++++++++++++++++-------------------------
> 3 files changed, 91 insertions(+), 78 deletions(-)
[...]
> diff --git a/symbols.c b/symbols.c
> index bf6d94d..44415da 100644
> --- a/symbols.c
> +++ b/symbols.c
[...]
> @@ -4494,53 +4561,14 @@ symbol_search(char *s)
> struct load_module *lm;
> int pseudos, search_init;
with big parts of the function removed some variables are no longer
used. Please remove their declaration.
> - 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);
> }
>
> /*
> @@ -5436,29 +5464,11 @@ symbol_exists(char *symbol)
> struct syment *sp, *sp_end;
> struct load_module *lm;
same like above.
Thanks
Philipp
> - 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 +5523,7 @@ 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 +5532,7 @@ 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 +12469,10 @@ 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 +12502,7 @@ 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 +12512,7 @@ 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 +12541,7 @@ 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 +12551,7 @@ 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;
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