Re: [PATCHv2 bpf-next 3/3] bpf: Change modules resolving for kprobe multi link

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Fri, Jan 13, 2023 at 6:44 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> We currently use module_kallsyms_on_each_symbol that iterates all
> modules/symbols and we try to lookup each such address in user
> provided symbols/addresses to get list of used modules.
>
> This fix instead only iterates provided kprobe addresses and calls
> __module_address on each to get list of used modules. This turned
> out to be simpler and also bit faster.
>
> On my setup with workload being (executed 10 times):
>
>    # test_progs -t kprobe_multi_bench_attach_module
>
> Current code:
>
>  Performance counter stats for './test.sh' (5 runs):
>
>     76,081,161,596      cycles:k                   ( +-  0.47% )
>
>            18.3867 +- 0.0992 seconds time elapsed  ( +-  0.54% )
>
> With the fix:
>
>  Performance counter stats for './test.sh' (5 runs):
>
>     74,079,889,063      cycles:k                   ( +-  0.04% )
>
>            17.8514 +- 0.0218 seconds time elapsed  ( +-  0.12% )
>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
>  kernel/trace/bpf_trace.c | 95 +++++++++++++++++++++-------------------
>  1 file changed, 49 insertions(+), 46 deletions(-)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 095f7f8d34a1..90c5d5026831 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2682,69 +2682,79 @@ 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 modules_array {
>         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 add_module(struct modules_array *arr, struct module *mod)
>  {
> -       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;
> -
> -       if (args->mods && args->mods[args->mods_cnt - 1] == mod)
> -               return 0;
> -
> -       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 (arr->mods_cnt == arr->mods_cap) {
> +               arr->mods_cap = max(16, arr->mods_cap * 3 / 2);
> +               mods = krealloc_array(arr->mods, arr->mods_cap, sizeof(*mods), GFP_KERNEL);
>                 if (!mods)
>                         return -ENOMEM;
> -               args->mods = mods;
> +               arr->mods = mods;
>         }
>
> -       if (!try_module_get(mod))
> -               return -EINVAL;
> -
> -       args->mods[args->mods_cnt] = mod;
> -       args->mods_cnt++;
> +       arr->mods[arr->mods_cnt] = mod;
> +       arr->mods_cnt++;
>         return 0;
>  }
>
> +static bool has_module(struct modules_array *arr, struct module *mod)
> +{
> +       int i;
> +
> +       if (!arr->mods)
> +               return false;
> +       for (i = arr->mods_cnt; i >= 0; i--) {

This should be "i = arr->mods_cnt - 1", no?

> +               if (arr->mods[i] == mod)
> +                       return true;
> +       }
> +       return false;
> +}
> +
>  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;
> +       struct modules_array arr = {};
> +       u32 i, err = 0;
> +
> +       for (i = 0; i < addrs_cnt; i++) {
> +               struct module *mod;
> +
> +               preempt_disable();
> +               mod = __module_address(addrs[i]);
> +               /* Either no module or we it's already stored  */
> +               if (!mod || (mod && has_module(&arr, mod))) {

nit: This can be simplified:

     if (!mod || has_module(&arr, mod)) {

> +                       preempt_enable();
> +                       continue;
> +               }

[...]



[Index of Archives]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]     [Big List of Linux Books]

  Powered by Linux