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path: root/gdb/filename-seen-cache.c
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2018-01-02Update copyright year range in all GDB filesJoel Brobecker1-1/+1
gdb/ChangeLog: Update copyright year range in all GDB files
2017-07-17Fix TAB-completion + .gdb_index slowness (generalize filename_seen_cache)Pedro Alves1-0/+66
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.