linker: Speed up relocation with an 1-entry symbol cache
When relocating a DSO, it is not unusual to have consecutive
relocations using the same symbol. In this case, it is wasteful to
perform the same symbol lookup. This change implements an 1-entry
symbol cache so that symbol lookup results are reused in such scenario.
Test: On cuttlefish, enable STATS in linker_debug.h. Boot and see RELO
STATS in logcat showing cache hits. Hit rate seen is mostly
within 15% to 45%.
Change-Id: I84783d3b9a6ac9e39ed7fb45e58f6b3c012478d0
diff --git a/linker/linker.cpp b/linker/linker.cpp
index ac7455b..e39da81 100644
--- a/linker/linker.cpp
+++ b/linker/linker.cpp
@@ -284,11 +284,13 @@
}
void print_linker_stats() {
- PRINT("RELO STATS: %s: %d abs, %d rel, %d copy, %d symbol", g_argv[0],
+ PRINT("RELO STATS: %s: %d abs, %d rel, %d copy, %d symbol (%d cached)",
+ g_argv[0],
linker_stats.count[kRelocAbsolute],
linker_stats.count[kRelocRelative],
linker_stats.count[kRelocCopy],
- linker_stats.count[kRelocSymbol]);
+ linker_stats.count[kRelocSymbol],
+ linker_stats.count[kRelocSymbolCached]);
}
#else
void count_relocation(RelocationKind) {
@@ -2891,6 +2893,17 @@
const size_t tls_tp_base = __libc_shared_globals()->static_tls_layout.offset_thread_pointer();
std::vector<std::pair<TlsDescriptor*, size_t>> deferred_tlsdesc_relocs;
+ struct {
+ // Cache key
+ ElfW(Word) sym;
+
+ // Cache value
+ const ElfW(Sym)* s;
+ soinfo* lsi;
+ } symbol_lookup_cache;
+
+ symbol_lookup_cache.sym = 0;
+
for (size_t idx = 0; rel_iterator.has_next(); ++idx) {
const auto rel = rel_iterator.next();
if (rel == nullptr) {
@@ -2934,14 +2947,25 @@
return false;
} else {
sym_name = get_string(symtab_[sym].st_name);
- const version_info* vi = nullptr;
- if (!lookup_version_info(version_tracker, sym, sym_name, &vi)) {
- return false;
- }
+ if (sym == symbol_lookup_cache.sym) {
+ s = symbol_lookup_cache.s;
+ lsi = symbol_lookup_cache.lsi;
+ count_relocation(kRelocSymbolCached);
+ } else {
+ const version_info* vi = nullptr;
- if (!soinfo_do_lookup(this, sym_name, vi, &lsi, global_group, local_group, &s)) {
- return false;
+ if (!lookup_version_info(version_tracker, sym, sym_name, &vi)) {
+ return false;
+ }
+
+ if (!soinfo_do_lookup(this, sym_name, vi, &lsi, global_group, local_group, &s)) {
+ return false;
+ }
+
+ symbol_lookup_cache.sym = sym;
+ symbol_lookup_cache.s = s;
+ symbol_lookup_cache.lsi = lsi;
}
if (s == nullptr) {