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authorChristian Biesinger <cbiesinger@google.com>2019-09-27 13:32:07 -0500
committerChristian Biesinger <cbiesinger@google.com>2019-10-22 11:47:24 -0500
commitccb1ba62299edce72053dd567b9d384814e11885 (patch)
tree2bea3a6796df3af2f866e854bef525d7a4d18b79 /gdb/utils.c
parent1a6ff1a96b302283d517b3cdeae7310adecbe859 (diff)
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Use libxxhash for hashing, if present
XXHash is faster than htab_hash_string: ------------------------------------------------------------ Benchmark Time CPU Iterations ------------------------------------------------------------ BM_xxh3 11 ns 11 ns 65887249 BM_xxh32 19 ns 19 ns 36511877 BM_xxh64 16 ns 16 ns 42964585 BM_hash_string 182 ns 182 ns 3853125 BM_iterative_hash 77 ns 77 ns 9087638 Unfortunately, XXH3 is still experimental (see https://github.com/Cyan4973/xxHash#user-content-new-experimental-hash-algorithm) However, regular XXH64 is still a lot faster than htab_hash_string per my benchmark above. I used the following string for the benchmark: static constexpr char str[] = "_ZZZL13make_gdb_typeP7gdbarchP10tdesc_typeEN16gdb_type_creator19make_gdb_type_flagsEPK22tdesc_type_with_fieldsE19__PRETTY_FUNCTION__"; htab_hash_string is currently 4.35% + 7.98% (rehashing) of gdb startup when attaching to Chrome's content_shell. An additional 5.21% is spent in msymbol_hash, which does not use this hash function. Unfortunately, since it has to lowercase the string, it can't use this hash function. BM_msymbol_hash 52 ns 52 ns 13281495 It may be worth investigating if strlen+XXHash is still faster than htab_hash_string, which would make it easier to use in more places. Debian ships xxhash as libxxhash{0,-dev}. Fedora ships it as xxhash-devel. gdb/ChangeLog: 2019-10-22 Christian Biesinger <cbiesinger@google.com> * Makefile.in: Link with libxxhash. * config.in: Regenerate. * configure: Regenerate. * configure.ac: Search for libxxhash. * utils.c (fast_hash): Use xxhash if present. Change-Id: Icab218388b9f829522ed3977f04301ae6d4fc4ca
Diffstat (limited to 'gdb/utils.c')
-rw-r--r--gdb/utils.c4
1 files changed, 4 insertions, 0 deletions
diff --git a/gdb/utils.c b/gdb/utils.c
index 3afb8e5..1b62e55 100644
--- a/gdb/utils.c
+++ b/gdb/utils.c
@@ -36,6 +36,10 @@
#include <pc.h>
#endif
+#ifdef HAVE_LIBXXHASH
+#include <xxhash.h>
+#endif
+
#include <signal.h>
#include "gdbcmd.h"
#include "serial.h"