forked from OSchip/llvm-project
df9a23e2fe
As shown in P2544R0 [1] and the accompanying benchmark [2], the current unwinding logic does not scale for multi-threaded programs. This is because `dl_iterate_phdr` takes a global lock. glibc 2.35 added `_dl_find_object` which directly returns the unwind info for a given target address. `_dl_find_object` is fully lock-free and hence allows parallel exception unwinding on multiple threads. With this commit, libunwind now takes advantage of `_dl_find_object`. Thereby, this commit improves libunwind's performance on benchmark [2] for unwinding exception on 20 threads from 1103ms to 78ms. (measured on Intel Xeon Silver 4114 with 20 physical cores) [1] https://isocpp.org/files/papers/P2544R0.html [2] https://github.com/neumannt/exceptionperformance Detailed performance numbers from the benchmark: Before: > Testing unwinding performance: sqrt computation with occasional errors > > testing baseline using 1 2 4 8 16 20 threads > failure rate 0%: 34 35 34 35 35 36 > testing exceptions using 1 2 4 8 16 20 threads > failure rate 0%: 16 32 33 34 35 36 > failure rate 0.1%: 16 32 34 36 35 36 > failure rate 1%: 20 40 40 43 90 113 > failure rate 10%: 59 92 140 304 880 1103 > [...] > > Testing invocation overhead: recursive fib with occasional errors > > testing exceptions using 1 2 4 8 16 20 threads > failure rate 0%: 19 32 37 38 39 36 > failure rate 0.1%: 22 32 40 40 39 34 > failure rate 1%: 20 28 38 39 48 40 > failure rate 10%: 25 39 44 50 92 113 After: > Testing unwinding performance: sqrt computation with occasional errors > > testing baseline using 1 2 4 8 16 20 threads > failure rate 0%: 19 30 35 38 39 35 > testing baseline using 1 2 4 8 16 20 threads > failure rate 0%: 32 35 33 34 34 36 > testing exceptions using 1 2 4 8 16 20 threads > failure rate 0%: 16 35 33 37 35 35 > failure rate 0.1%: 16 32 36 33 34 37 > failure rate 1%: 21 37 39 40 40 41 > failure rate 10%: 72 75 76 80 80 78 > [...] > > Testing invocation overhead: recursive fib with occasional errors > > testing baseline using 1 2 4 8 16 20 threads > failure rate 0%: 18 35 37 34 38 37 > testing exceptions using 1 2 4 8 16 20 threads > failure rate 0%: 19 33 40 40 41 39 > failure rate 0.1%: 21 33 39 38 39 38 > failure rate 1%: 20 36 39 40 41 40 > failure rate 10%: 25 45 41 42 44 43 Differential Revision: https://reviews.llvm.org/D130668 |
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