Update after lookup in map.increment for HASH types

Performing the update before lookup incurs an extra spinlock in the kernel, which hurts performance. Reorder the code and increment to 1. The memset is there I believe due to some type mismatch warnings, so I'm leaving as is rather than doing a direct assign to 1. The resulting code is optimized away anyway. Fixes: iovisor#1314 Signed-off-by: Brenden Blanco <[email protected]>
drcwr · Aug 25, 2017 · 23fc589 · 23fc589
1 parent 917f4c7
commit 23fc589
Showing 1 changed file with 6 additions and 4 deletions.
diff --git a/src/cc/frontends/clang/b_frontend_action.cc b/src/cc/frontends/clang/b_frontend_action.cc
@@ -332,12 +332,14 @@ bool BTypeVisitor::VisitCallExpr(CallExpr *Call) {
  string lookup = "bpf_map_lookup_elem_(bpf_pseudo_fd(1, " + fd + ")";
  string update = "bpf_map_update_elem_(bpf_pseudo_fd(1, " + fd + ")";
  txt = "({ typeof(" + name + ".key) _key = " + arg0 + "; ";
+ txt += "typeof(" + name + ".leaf) *_leaf = " + lookup + ", &_key); ";
+ txt += "if (_leaf) (*_leaf)++; ";
  if (desc->second.type == BPF_MAP_TYPE_HASH) {
- txt += "typeof(" + name + ".leaf) _zleaf; memset(&_zleaf, 0, sizeof(_zleaf)); ";
- txt += update + ", &_key, &_zleaf, BPF_NOEXIST); ";
+ txt += "else { typeof(" + name + ".leaf) _zleaf; memset(&_zleaf, 0, sizeof(_zleaf)); ";
+ txt += "_zleaf++; ";
+ txt += update + ", &_key, &_zleaf, BPF_NOEXIST); } ";
  }
- txt += "typeof(" + name + ".leaf) *_leaf = " + lookup + ", &_key); ";
- txt += "if (_leaf) (*_leaf)++; })";
+ txt += "})";
  } else if (memb_name == "perf_submit") {
  string name = Ref->getDecl()->getName();
  string arg0 = rewriter_.getRewrittenText(expansionRange(Call->getArg(0)->getSourceRange()));