[PATCH v3 7/8] Demangle minsyms in parallel

Tom Tromey
2019-05-29T21:29:29Z

This patch introduces a simple parallel for_each and changes the
minimal symbol reader to use it when computing the demangled name for
a minimal symbol. This yields a speedup when reading minimal symbols.

gdb/ChangeLog
2019-05-29 Tom Tromey <tom@tromey.com>

* minsyms.c (minimal_symbol_reader::install): Use
parallel_for_each.
* common/parallel-for.h: New file.
* common/parallel-for.c: New file.
* Makefile.in (HFILES_NO_SRCDIR): Add common/parallel-for.h.
(COMMON_SFILES): Add common/parallel-for.c.
---
gdb/ChangeLog | 9 +++++
gdb/Makefile.in | 2 +
gdb/common/parallel-for.c | 27 +++++++++++++
gdb/common/parallel-for.h | 82 +++++++++++++++++++++++++++++++++++++++
gdb/minsyms.c | 23 ++++++-----
5 files changed, 133 insertions(+), 10 deletions(-)
create mode 100644 gdb/common/parallel-for.c
create mode 100644 gdb/common/parallel-for.h

diff --git a/gdb/Makefile.in b/gdb/Makefile.in
index 2dd69f3f0ba..15c7a6e2536 100644
--- a/gdb/Makefile.in
+++ b/gdb/Makefile.in
@@ -971,6 +971,7 @@ COMMON_SFILES = \
common/gdb_vecs.c \
common/netstuff.c \
common/new-op.c \
+ common/parallel-for.c \
common/pathstuff.c \
common/print-utils.c \
common/ptid.c \
@@ -1471,6 +1472,7 @@ HFILES_NO_SRCDIR = \
common/common-inferior.h \
common/netstuff.h \
common/host-defs.h \
+ common/parallel-for.h \
common/pathstuff.h \
common/print-utils.h \
common/ptid.h \
diff --git a/gdb/common/parallel-for.c b/gdb/common/parallel-for.c
new file mode 100644
index 00000000000..0970cea882b
--- /dev/null
+++ b/gdb/common/parallel-for.c
@@ -0,0 +1,27 @@
+/* Parallel for loops
+
+ Copyright (C) 2019 Free Software Foundation, Inc.
+
+ This file is part of GDB.
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <http://www.gnu.org/licenses/>. */
+
+#include "common/common-defs.h"
+#include "common/parallel-for.h"
+
+namespace gdb
+{
+/* See parallel-for.h. */
+int max_threads = -1;
+}
diff --git a/gdb/common/parallel-for.h b/gdb/common/parallel-for.h
new file mode 100644
index 00000000000..6770f39a05f
--- /dev/null
+++ b/gdb/common/parallel-for.h
@@ -0,0 +1,82 @@
+/* Parallel for loops
+
+ Copyright (C) 2019 Free Software Foundation, Inc.
+
+ This file is part of GDB.
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <http://www.gnu.org/licenses/>. */
+
+#ifndef COMMON_PARALLEL_FOR_H
+#define COMMON_PARALLEL_FOR_H
+
+#include <algorithm>
+#if CXX_STD_THREAD
+#include <thread>
+#endif
+
+namespace gdb
+{
+
+/* True if threading should be enabled. */
+
+extern int max_threads;
+
+/* A very simple "parallel for". This iterates over the elements
+ given by the range of iterators, which must be random access
+ iterators. For each element, it calls the callback function. The
+ work may or may not be done by separate threads. */
+
+template<class RandomIt, class UnaryFunction>
+void parallel_for_each (RandomIt first, RandomIt last, UnaryFunction f)
+{
+#if CXX_STD_THREAD
+ int n_threads = std::thread::hardware_concurrency ();
+ /* So we can use a local array below. */
+ const int local_max = 16;
+ /* Be sure to handle the "unlimited" case. */
+ if (max_threads >= 0 && n_threads > max_threads)
+ n_threads = max_threads;
+ if (n_threads > local_max)
+ n_threads = local_max;
+
+ if (n_threads <= 1 || last - first < 2 * n_threads)
+#endif /* CXX_STD_THREAD */
+ {
+ /* Don't bother. */
+ std::for_each (first, last, f);
+ return;
+ }
+
+#if CXX_STD_THREAD
+ auto body = [&] (RandomIt start)
+ {
+ for (; start < last; start += n_threads)
+ f (*start);
+ };
+
+ std::thread threads[local_max];
+ for (int i = 0; i < n_threads; ++i)
+ {
+ threads[i] = std::thread (body, first);
+ ++first;
+ }
+
+ for (int i = 0; i < n_threads; ++i)
+ threads[i].join ();
+#endif /* CXX_STD_THREAD */
+}
+
+}
+
+#endif /* COMMON_PARALLEL_FOR_H */
diff --git a/gdb/minsyms.c b/gdb/minsyms.c
index 488201a1886..4c0ee11c47e 100644
--- a/gdb/minsyms.c
+++ b/gdb/minsyms.c
@@ -53,6 +53,7 @@
#include "common/symbol.h"
#include <algorithm>
#include "safe-ctype.h"
+#include "common/parallel-for.h"

/* See minsyms.h. */

@@ -1372,16 +1373,18 @@ minimal_symbol_reader::install ()
m_objfile->per_bfd->msymbols = std::move (msym_holder);

msymbols = m_objfile->per_bfd->msymbols.get ();
- for (int i = 0; i < mcount; ++i)
- {
- if (!msymbols[i].name_set)
- {
- symbol_set_names (&msymbols[i], msymbols[i].name,
- strlen (msymbols[i].name), 0,
- m_objfile->per_bfd);
- msymbols[i].name_set = 1;
- }
- }
+ gdb::parallel_for_each
+ (&msymbols[0], &msymbols[mcount],
+ [&] (minimal_symbol &msym)
+ {
+ if (!msym.name_set)
+ {
+ symbol_set_names (&msym, msym.name,
+ strlen (msym.name), 0,
+ m_objfile->per_bfd);
+ msym.name_set = 1;
+ }
+ });

build_minimal_symbol_hash_tables (m_objfile);
}
--
2.17.2