Re: [RFC bpf-next 07/16] kallsyms: Use rb tree for kallsyms name search

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Wed, Oct 28, 2020 at 3:29 PM Jiri Olsa <jolsa@redhat.com> wrote:
>
> On Thu, Oct 22, 2020 at 10:21:29AM +0200, Jiri Olsa wrote:
> > The kallsyms_expand_symbol function showed in several bpf related
> > profiles, because it's doing linear search.
> >
> > Before:
> >
> >  Performance counter stats for './src/bpftrace -ve kfunc:__x64_sys_s* \
> >    { printf("test\n"); } i:ms:10 { printf("exit\n"); exit();}' (5 runs):
> >
> >      2,535,458,767      cycles:k                         ( +-  0.55% )
> >        940,046,382      cycles:u                         ( +-  0.27% )
> >
> >              33.60 +- 3.27 seconds time elapsed  ( +-  9.73% )
> >
> > Loading all the vmlinux symbols in rbtree and and switch to rbtree
> > search in kallsyms_lookup_name function to save few cycles and time.
> >
> > After:
> >
> >  Performance counter stats for './src/bpftrace -ve kfunc:__x64_sys_s* \
> >    { printf("test\n"); } i:ms:10 { printf("exit\n"); exit();}' (5 runs):
> >
> >      2,199,433,771      cycles:k                         ( +-  0.55% )
> >        936,105,469      cycles:u                         ( +-  0.37% )
> >
> >              26.48 +- 3.57 seconds time elapsed  ( +- 13.49% )
> >
> > Each symbol takes 160 bytes, so for my .config I've got about 18 MBs
> > used for 115285 symbols.
> >
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
>
> FYI there's init_kprobes dependency on kallsyms_lookup_name in early
> init call, so this won't work as it is :-\ will address this in v2
>
> also I'll switch to sorted array and bsearch, because kallsyms is not
> dynamically updated

what about kernel modules then?

>
> jirka
>
> > ---
> >  kernel/kallsyms.c | 95 ++++++++++++++++++++++++++++++++++++++++++-----
> >  1 file changed, 86 insertions(+), 9 deletions(-)
> >

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