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H A D | btf.c | d81283d2 Wed Jan 19 12:02:14 CST 2022 Kui-Feng Lee <kuifeng@fb.com> libbpf: Improve btf__add_btf() with an additional hashmap for strings.
Add a hashmap to map the string offsets from a source btf to the string offsets from a target btf to reduce overheads.
btf__add_btf() calls btf__add_str() to add strings from a source to a target btf. It causes many string comparisons, and it is a major hotspot when adding a big btf. btf__add_str() uses strcmp() to check if a hash entry is the right one. The extra hashmap here compares offsets of strings, that are much cheaper. It remembers the results of btf__add_str() for later uses to reduce the cost.
We are parallelizing BTF encoding for pahole by creating separated btf instances for worker threads. These per-thread btf instances will be added to the btf instance of the main thread by calling btf__add_str() to deduplicate and write out. With this patch and -j4, the running time of pahole drops to about 6.0s from 6.6s.
The following lines are the summary of 'perf stat' w/o the change.
6.668126396 seconds time elapsed
13.451054000 seconds user 0.715520000 seconds sys
The following lines are the summary w/ the change.
5.986973919 seconds time elapsed
12.939903000 seconds user 0.724152000 seconds sys
V4 fixes a bug of error checking against the pointer returned by hashmap__new().
[v3] https://lore.kernel.org/bpf/20220118232053.2113139-1-kuifeng@fb.com/ [v2] https://lore.kernel.org/bpf/20220114193713.461349-1-kuifeng@fb.com/
Signed-off-by: Kui-Feng Lee <kuifeng@fb.com> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20220119180214.255634-1-kuifeng@fb.com
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