On 2023/1/6 5:31, Jiri Olsa wrote: > On Wed, Jan 04, 2023 at 05:25:08PM +0100, Petr Mladek wrote: >> On Fri 2022-12-30 19:27:28, Zhen Lei wrote: >>> Function __module_address() can quickly return the pointer of the module >>> to which an address belongs. We do not need to traverse the symbols of all >>> modules to check whether each address in addrs[] is the start address of >>> the corresponding symbol, because register_fprobe_ips() will do this check >>> later. > > hum, for some reason I can see only replies to this patch and > not the actual patch.. I'll dig it out of the lore I guess https://lkml.org/lkml/2022/12/30/195 > >>> >>> Assuming that there are m modules, each module has n symbols on average, >>> and the number of addresses 'addrs_cnt' is abbreviated as K. Then the time >>> complexity of the original method is O(K * log(K)) + O(m * n * log(K)), >>> and the time complexity of current method is O(K * (log(m) + M)), M <= m. >>> (m * n * log(K)) / (K * m) ==> n / log2(K). Even if n is 10 and K is 128, >>> the ratio is still greater than 1. Therefore, the new method will >>> generally have better performance. > > could you try to benchmark that? I tried something similar but was not > able to get better performance I'm just theoretically analyzing, at least the performance won't get worse. > > I'll review and run my benchmark test tomorrow > > thanks, > jirka > >>> >>> Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx> >>> --- >>> kernel/trace/bpf_trace.c | 101 ++++++++++++++++----------------------- >>> 1 file changed, 40 insertions(+), 61 deletions(-) >>> >>> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c >>> index 5f3be4bc16403a5..0ff9037098bd241 100644 >>> --- a/kernel/trace/bpf_trace.c >>> +++ b/kernel/trace/bpf_trace.c >>> @@ -2684,69 +2684,55 @@ static void symbols_swap_r(void *a, void *b, int size, const void *priv) >>> } >>> } >>> >>> -struct module_addr_args { >>> - unsigned long *addrs; >>> - u32 addrs_cnt; >>> - struct module **mods; >>> - int mods_cnt; >>> - int mods_cap; >>> -}; >>> - >>> -static int module_callback(void *data, const char *name, >>> - struct module *mod, unsigned long addr) >>> +static int get_modules_for_addrs(struct module ***out_mods, unsigned long *addrs, u32 addrs_cnt) >>> { >>> - struct module_addr_args *args = data; >>> - struct module **mods; >>> - >>> - /* We iterate all modules symbols and for each we: >>> - * - search for it in provided addresses array >>> - * - if found we check if we already have the module pointer stored >>> - * (we iterate modules sequentially, so we can check just the last >>> - * module pointer) >>> - * - take module reference and store it >>> - */ >>> - if (!bsearch(&addr, args->addrs, args->addrs_cnt, sizeof(addr), >>> - bpf_kprobe_multi_addrs_cmp)) >>> - return 0; >>> + int i, j, err; >>> + int mods_cnt = 0; >>> + int mods_cap = 0; >>> + struct module *mod; >>> + struct module **mods = NULL; >>> >>> - if (args->mods && args->mods[args->mods_cnt - 1] == mod) >>> - return 0; >>> + for (i = 0; i < addrs_cnt; i++) { >>> + mod = __module_address(addrs[i]); >> >> This must be called under module_mutex to make sure that the module >> would not disappear. >> >>> + if (!mod) >>> + continue; >>> >>> - if (args->mods_cnt == args->mods_cap) { >>> - args->mods_cap = max(16, args->mods_cap * 3 / 2); >>> - mods = krealloc_array(args->mods, args->mods_cap, sizeof(*mods), GFP_KERNEL); >>> - if (!mods) >>> - return -ENOMEM; >>> - args->mods = mods; >>> - } >>> + /* check if we already have the module pointer stored */ >>> + for (j = 0; j < mods_cnt; j++) { >>> + if (mods[j] == mod) >>> + break; >>> + } >> >> This might get optimized like the original code. >> >> My understanding is that the addresses are sorted in "addrs" array. >> So, the address is either part of the last found module or it belongs >> to a completely new module. >> >> for (i = 0; i < addrs_cnt; i++) { >> /* >> * The adresses are sorted. The adress either belongs >> * to the last found module or a new one. >> * >> * This is safe because we already have reference >> * on the found modules. >> */ >> if (mods_cnt && within_module(addrs[i], mods[mods_cnt - 1])) >> continue; >> >> mutex_lock(&module_mutex); >> mod = __module_address(addrs[i]); >> if (mod && !try_module_get(mod)) { >> mutex_unlock(&module_mutex); >> goto failed; >> } >> mutex_unlock(&module_mutex); >> >> /* >> * Nope when the address was not from a module. >> * >> * Is this correct? What if the module has gone in >> * the meantime? Anyway, the original code >> * worked this way. >> * >> * FIXME: I would personally make sure that it is part >> * of vmlinux or so. >> */ >> if (!mod) >> continue; >> >> /* store the module into mods array */ >> ... >> >> >> >> >>> + if (j < mods_cnt) >>> + continue; >>> >>> - if (!try_module_get(mod)) >>> - return -EINVAL; >>> + if (mods_cnt == mods_cap) { >>> + struct module **new_mods; >>> >>> - args->mods[args->mods_cnt] = mod; >>> - args->mods_cnt++; >>> - return 0; >>> -} >>> + mods_cap = max(16, mods_cap * 3 / 2); >>> + new_mods = krealloc_array(mods, mods_cap, sizeof(*mods), GFP_KERNEL); >>> + if (!new_mods) { >>> + err = -ENOMEM; >>> + goto failed; >>> + } >>> + mods = new_mods; >>> + } >>> >>> -static int get_modules_for_addrs(struct module ***mods, unsigned long *addrs, u32 addrs_cnt) >>> -{ >>> - struct module_addr_args args = { >>> - .addrs = addrs, >>> - .addrs_cnt = addrs_cnt, >>> - }; >>> - int err; >>> + if (!try_module_get(mod)) { >>> + err = -EINVAL; >>> + goto failed; >>> + } >>> >>> - /* We return either err < 0 in case of error, ... */ >>> - err = module_kallsyms_on_each_symbol(NULL, module_callback, &args); >>> - if (err) { >>> - kprobe_multi_put_modules(args.mods, args.mods_cnt); >>> - kfree(args.mods); >>> - return err; >>> + mods[mods_cnt] = mod; >>> + mods_cnt++; >>> } >>> >>> - /* or number of modules found if everything is ok. */ >>> - *mods = args.mods; >>> - return args.mods_cnt; >>> + *out_mods = mods; >>> + return mods_cnt; >>> + >>> +failed: >>> + kprobe_multi_put_modules(mods, mods_cnt); >>> + kfree(mods); >>> + return err; >>> } >>> >>> int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog) >> >> Otherwise, it looks good. IMHO, the new code looks more straightforward >> than the original one. >> >> Best Regards, >> Petr > . > -- Regards, Zhen Lei
