On Wed, Oct 28, 2020 at 03:40:46PM -0700, Andrii Nakryiko wrote:
> On Wed, Oct 28, 2020 at 3:29 PM Jiri Olsa <jolsa@xxxxxxxxxx> 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@xxxxxxxxxx>
> >
> > 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?
please check my answer to Alexei, I just answered it there
thanks,
jirka
>
> >
> > jirka
> >
> > > ---
> > > kernel/kallsyms.c | 95 ++++++++++++++++++++++++++++++++++++++++++-----
> > > 1 file changed, 86 insertions(+), 9 deletions(-)
> > >
>
> [...]
>
