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| author | Christian Biesinger <cbiesinger@google.com> | 2019-09-27 13:32:07 -0500 |
|---|---|---|
| committer | Christian Biesinger <cbiesinger@google.com> | 2019-10-22 11:47:24 -0500 |
| commit | ccb1ba62299edce72053dd567b9d384814e11885 (patch) | |
| tree | 2bea3a6796df3af2f866e854bef525d7a4d18b79 /gdb/configure.ac | |
| parent | 1a6ff1a96b302283d517b3cdeae7310adecbe859 (diff) | |
| download | gdb-ccb1ba62299edce72053dd567b9d384814e11885.zip gdb-ccb1ba62299edce72053dd567b9d384814e11885.tar.gz gdb-ccb1ba62299edce72053dd567b9d384814e11885.tar.bz2 | |
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/configure.ac')
| -rw-r--r-- | gdb/configure.ac | 23 |
1 files changed, 23 insertions, 0 deletions
diff --git a/gdb/configure.ac b/gdb/configure.ac index dbe0150..6297502 100644 --- a/gdb/configure.ac +++ b/gdb/configure.ac @@ -2217,6 +2217,29 @@ else fi fi +# Check for xxhash +AC_ARG_WITH(xxhash, + AC_HELP_STRING([--with-xxhash], [use libxxhash for hashing (faster) (auto/yes/no)]), + [], [with_xxhash=auto]) + +if test "x$with_xxhash" != "xno"; then + AC_LIB_HAVE_LINKFLAGS([xxhash], [], + [#include <xxhash.h>], + [XXH32("foo", 3, 0); + ]) + if test "$HAVE_LIBXXHASH" != yes; then + if test "$with_xxhash" = yes; then + AC_MSG_ERROR([xxhash is missing or unusable]) + fi + fi + if test "x$with_xxhash" = "xauto"; then + with_xxhash="$HAVE_LIBXXHASH" + fi +fi + +AC_MSG_CHECKING([whether to use xxhash]) +AC_MSG_RESULT([$with_xxhash]) + NM_H= rm -f nm.h if test "${nativefile}" != ""; then |