Messages in this thread | | | From | Hao Luo <> | Date | Thu, 10 Mar 2022 17:16:10 -0800 | Subject | Re: [PATCH bpf-next v2] bpf: Cache the last valid build_id. |
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On Fri, Feb 25, 2022 at 12:43 PM Pasha Tatashin <pasha.tatashin@soleen.com> 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@google.com> > > Signed-off-by: Hao Luo <haoluo@google.com> > > Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com> >
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
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