On Fri, Feb 25, 2022 at 12:43 PM Pasha Tatashin
<pasha.tatashin@xxxxxxxxxx> wrote:
>
> On 2/23/22 19:05, Hao Luo wrote:
> > For binaries that are statically linked, consecutive stack frames are
> > likely to be in the same VMA and therefore have the same build id.
> > As an optimization for this case, we can cache the previous frame's
> > VMA, if the new frame has the same VMA as the previous one, reuse the
> > previous one's build id. We are holding the MM locks as reader across
> > the entire loop, so we don't need to worry about VMA going away.
> >
> > Tested through "stacktrace_build_id" and "stacktrace_build_id_nmi" in
> > test_progs.
> >
> > Suggested-by: Greg Thelen <gthelen@xxxxxxxxxx>
> > Signed-off-by: Hao Luo <haoluo@xxxxxxxxxx>
>
> Reviewed-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
>
An update with performance numbers. Thanks to Blake Jones for
collecting the stats:
In a production workload, with BPF probes sampling stack trace, we see
the following changes:
- stack_map_get_build_id_offset() is taking 70% of the time of
__bpf_get_stackid(); it was 80% before.
- find_get_page() and find_vma() together are taking 75% of the time
of stack_map_get_build_id_offset(); it was 83% before.
Note the call chain is
__bpf_get_stackid()
-> stack_map_get_build_id_offset()
-> find_get_page()
-> find_vma()
> Thanks,
> Pasha
