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In commitc4a122ead6("libdrgn: dwarf_info: scalably index all DIEs per name"), I noted that indexing the Linux kernel was slower with 80 threads than with 8. After experimenting on multiple systems, I determined that the slowdown was because of hyperthreading; limiting the number of threads to the number of cores (not hyperthreads) was usually faster, and never slower. Unfortunately, OpenMP doesn't have a convenient way to express this, so we have to parse sysfs and explicitly specify the number of threads ourselves. Compared to commitc4a122ead6("libdrgn: dwarf_info: scalably index all DIEs per name"), this makes indexing the large C++ application half a second faster, and the Linux kernel 70 ms faster, all while using less resources. Signed-off-by: Omar Sandoval <osandov@osandov.com>
21 lines
358 B
C
21 lines
358 B
C
// Copyright (c) Meta Platforms, Inc. and affiliates.
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// SPDX-License-Identifier: LGPL-2.1-or-later
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#ifndef DRGN_OPENMP_H
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#define DRGN_OPENMP_H
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#ifdef _OPENMP
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#include <omp.h> // IWYU pragma: export
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extern int drgn_num_threads;
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#else
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static inline int omp_get_thread_num(void)
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{
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return 0;
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}
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#define drgn_num_threads 1
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#endif
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#endif /* DRGN_OPENMP_H */
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