forked from Imagelibrary/binutils-gdb
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.
This commit is contained in:
Pedro Alves
100
gdb/symtab.c
100
gdb/symtab.c
@@ -63,6 +63,7 @@
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#include "completer.h"
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#include "progspace-and-thread.h"
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#include "common/gdb_optional.h"
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#include "filename-seen-cache.h"
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/* Forward declarations for local functions. */
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@@ -3968,74 +3969,6 @@ operator_chars (const char *p, const char **end)
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}
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/* Cache to watch for file names already seen by filename_seen. */
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struct filename_seen_cache
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{
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/* Table of files seen so far. */
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htab_t tab;
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/* Initial size of the table. It automagically grows from here. */
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#define INITIAL_FILENAME_SEEN_CACHE_SIZE 100
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};
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/* filename_seen_cache constructor. */
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static struct filename_seen_cache *
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create_filename_seen_cache (void)
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{
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struct filename_seen_cache *cache = XNEW (struct filename_seen_cache);
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cache->tab = htab_create_alloc (INITIAL_FILENAME_SEEN_CACHE_SIZE,
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filename_hash, filename_eq,
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NULL, xcalloc, xfree);
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return cache;
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}
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/* Empty the cache, but do not delete it. */
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static void
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clear_filename_seen_cache (struct filename_seen_cache *cache)
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{
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htab_empty (cache->tab);
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}
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/* filename_seen_cache destructor.
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This takes a void * argument as it is generally used as a cleanup. */
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static void
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delete_filename_seen_cache (void *ptr)
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{
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struct filename_seen_cache *cache = (struct filename_seen_cache *) ptr;
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htab_delete (cache->tab);
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xfree (cache);
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}
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/* If FILE is not already in the table of files in CACHE, return zero;
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otherwise return non-zero. Optionally add FILE to the table if ADD
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is non-zero.
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NOTE: We don't manage space for FILE, we assume FILE lives as long
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as the caller needs. */
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static int
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filename_seen (struct filename_seen_cache *cache, const char *file, int add)
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{
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void **slot;
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/* Is FILE in tab? */
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slot = htab_find_slot (cache->tab, file, add ? INSERT : NO_INSERT);
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if (*slot != NULL)
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return 1;
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/* No; maybe add it to tab. */
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if (add)
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*slot = (char *) file;
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return 0;
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}
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/* Data structure to maintain printing state for output_source_filename. */
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struct output_source_filename_data
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@@ -4065,7 +3998,7 @@ output_source_filename (const char *name,
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symtabs; it doesn't hurt to check. */
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/* Was NAME already seen? */
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if (filename_seen (data->filename_seen_cache, name, 1))
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if (data->filename_seen_cache->seen (name))
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{
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/* Yes; don't print it again. */
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return;
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@@ -4097,16 +4030,15 @@ sources_info (char *ignore, int from_tty)
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struct symtab *s;
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struct objfile *objfile;
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struct output_source_filename_data data;
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struct cleanup *cleanups;
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if (!have_full_symbols () && !have_partial_symbols ())
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{
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error (_("No symbol table is loaded. Use the \"file\" command."));
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}
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data.filename_seen_cache = create_filename_seen_cache ();
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cleanups = make_cleanup (delete_filename_seen_cache,
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data.filename_seen_cache);
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filename_seen_cache filenames_seen;
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data.filename_seen_cache = &filenames_seen;
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printf_filtered ("Source files for which symbols have been read in:\n\n");
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@@ -4122,13 +4054,11 @@ sources_info (char *ignore, int from_tty)
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printf_filtered ("Source files for which symbols "
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"will be read in on demand:\n\n");
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clear_filename_seen_cache (data.filename_seen_cache);
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filenames_seen.clear ();
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data.first = 1;
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map_symbol_filenames (output_partial_symbol_filename, &data,
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1 /*need_fullname*/);
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printf_filtered ("\n");
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do_cleanups (cleanups);
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}
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/* Compare FILE against all the NFILES entries of FILES. If BASENAMES is
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@@ -5552,7 +5482,7 @@ maybe_add_partial_symtab_filename (const char *filename, const char *fullname,
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if (not_interesting_fname (filename))
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return;
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if (!filename_seen (data->filename_seen_cache, filename, 1)
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if (!data->filename_seen_cache->seen (filename)
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&& filename_ncmp (filename, data->text, data->text_len) == 0)
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{
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/* This file matches for a completion; add it to the
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@@ -5564,7 +5494,7 @@ maybe_add_partial_symtab_filename (const char *filename, const char *fullname,
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const char *base_name = lbasename (filename);
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if (base_name != filename
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&& !filename_seen (data->filename_seen_cache, base_name, 1)
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&& !data->filename_seen_cache->seen (base_name)
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&& filename_ncmp (base_name, data->text, data->text_len) == 0)
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add_filename_to_list (base_name, data->text, data->word, data->list);
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}
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@@ -5585,23 +5515,20 @@ make_source_files_completion_list (const char *text, const char *word)
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VEC (char_ptr) *list = NULL;
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const char *base_name;
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struct add_partial_filename_data datum;
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struct filename_seen_cache *filename_seen_cache;
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struct cleanup *back_to, *cache_cleanup;
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struct cleanup *back_to;
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if (!have_full_symbols () && !have_partial_symbols ())
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return list;
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back_to = make_cleanup (do_free_completion_list, &list);
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filename_seen_cache = create_filename_seen_cache ();
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cache_cleanup = make_cleanup (delete_filename_seen_cache,
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filename_seen_cache);
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filename_seen_cache filenames_seen;
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ALL_FILETABS (objfile, cu, s)
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{
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if (not_interesting_fname (s->filename))
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continue;
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if (!filename_seen (filename_seen_cache, s->filename, 1)
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if (!filenames_seen.seen (s->filename)
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&& filename_ncmp (s->filename, text, text_len) == 0)
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{
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/* This file matches for a completion; add it to the current
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@@ -5616,13 +5543,13 @@ make_source_files_completion_list (const char *text, const char *word)
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command do when they parse file names. */
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base_name = lbasename (s->filename);
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if (base_name != s->filename
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&& !filename_seen (filename_seen_cache, base_name, 1)
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&& !filenames_seen.seen (base_name)
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&& filename_ncmp (base_name, text, text_len) == 0)
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add_filename_to_list (base_name, text, word, &list);
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}
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}
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datum.filename_seen_cache = filename_seen_cache;
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datum.filename_seen_cache = &filenames_seen;
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datum.text = text;
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datum.word = word;
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datum.text_len = text_len;
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@@ -5630,7 +5557,6 @@ make_source_files_completion_list (const char *text, const char *word)
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map_symbol_filenames (maybe_add_partial_symtab_filename, &datum,
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0 /*need_fullname*/);
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do_cleanups (cache_cleanup);
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discard_cleanups (back_to);
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return list;
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