binutils-gdb/gdb/filename-seen-cache.h

64 lines
1.9 KiB
C
Raw Normal View History

Fix TAB-completion + .gdb_index slowness (generalize filename_seen_cache) Tab completion when debugging a program binary that uses GDB index is surprisingly much slower than when GDB uses psymtabs instead. Around 1.5x/3x slower. That's surprising, because the whole point of GDB index is to speed things up... For example, with: set pagination off set $count = 0 while $count < 400 complete b string_prin # matches gdb's string_printf printf "count = %d\n", $count set $count = $count + 1 end $ time ./gdb --batch -q ./gdb-with-index -ex "source script.cmd" real 0m11.042s user 0m10.920s sys 0m0.042s $ time ./gdb --batch -q ./gdb-without-index -ex "source script.cmd" real 0m4.635s user 0m4.590s sys 0m0.037s Same but with: - complete b string_prin + complete b zzzzzz to exercise the no-matches worst case, master currently gets you something like: with index without index real 0m11.971s 0m8.413s user 0m11.912s 0m8.355s sys 0m0.035s 0m0.035s Running gdb under perf shows 80% spent inside maybe_add_partial_symtab_filename, and 20% spent in the lbasename inside that. The problem that tab completion walks over all compunit symtabs, and for each, walks the contained file symtabs. And there a huge number of file symtabs (each included system header, etc.) that appear in each compunit symtab's file symtab list. As in, when debugging GDB, I have 367381 symtabs iterated, when of those only 5371 filenames are unique... This was a regression from the earlier (nice) split of symtabs in compunit symtabs + file symtabs. The fix here is to add a cache of unique filenames per objfile so that the walk / uniquing is only done once. There's already a abstraction for this in symtab.c; this patch moves that code out to a separate file and C++ifies it bit. This makes the worst-case scenario above consistently drop to ~2.5s (1.5s for the "string_prin" hit case), making it over 3.3x times faster than psymtabs in this use case (7x in the "string_prin" hit case). gdb/ChangeLog: 2017-07-17 Pedro Alves <palves@redhat.com> * Makefile.in (COMMON_OBS): Add filename-seen-cache.o. * dwarf2read.c: Include "filename-seen-cache.h". * dwarf2read.c (dwarf2_per_objfile) <filenames_cache>: New field. (dw2_map_symbol_filenames): Build and use a filenames_seen_cache. * filename-seen-cache.c: New file. * filename-seen-cache.h: New file. * symtab.c: Include "filename-seen-cache.h". (struct filename_seen_cache, INITIAL_FILENAME_SEEN_CACHE_SIZE) (create_filename_seen_cache, clear_filename_seen_cache) (delete_filename_seen_cache, filename_seen): Delete, parts moved to filename-seen-cache.h/filename-seen-cache.c. (output_source_filename, sources_info) (maybe_add_partial_symtab_filename) (make_source_files_completion_list): Adjust to use filename_seen_cache.
2017-07-17 12:28:33 +02:00
/* Filename-seen cache for the GNU debugger, GDB.
Copyright (C) 1986-2017 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 "defs.h"
#include "common/function-view.h"
/* Cache to watch for file names already seen. */
class filename_seen_cache
{
public:
filename_seen_cache ();
~filename_seen_cache ();
/* Disable copy. */
filename_seen_cache (const filename_seen_cache &) = delete;
void operator= (const filename_seen_cache &) = delete;
/* Empty the cache, but do not delete it. */
void clear ();
/* If FILE is not already in the table of files in CACHE, add it and
return false; otherwise return true.
NOTE: We don't manage space for FILE, we assume FILE lives as
long as the caller needs. */
bool seen (const char *file);
/* Traverse all cache entries, calling CALLBACK on each. The
filename is passed as argument to CALLBACK. */
void traverse (gdb::function_view<void (const char *filename)> callback)
{
auto erased_cb = [] (void **slot, void *info) -> int
{
auto filename = (const char *) *slot;
auto restored_cb = (decltype (callback) *) info;
(*restored_cb) (filename);
return 1;
};
htab_traverse_noresize (m_tab, erased_cb, &callback);
}
private:
/* Table of files seen so far. */
htab_t m_tab;
};