Add counters to measure branch_stub_hit instances on old ISEQs

yjit.rb

@@ -285,6 +285,9 @@ def _print_stats(out: $stderr) # :nodoc:
  if stats[:compiled_blockid_count] != 0
  out.puts "versions_per_block: " + ("%10.3f" % stats[:compiled_block_count].fdiv(stats[:compiled_blockid_count]))
  end
+ out.puts "branch_stub_hit: " + ("%10d" % stats[:branch_stub_hit])
+ out.puts "branch_stub_hit_old: " + ("%10d" % stats[:branch_stub_hit_old])
+
  out.puts "compiled_branch_count: " + ("%10d" % stats[:compiled_branch_count])
  out.puts "compile_time_ms: " + ("%10d" % stats[:compile_time_ns].div(1000 * 1000))
  out.puts "block_next_count: " + ("%10d" % stats[:block_next_count])

yjit/src/core.rs

@@ -535,6 +535,10 @@ pub struct IseqPayload {
  // Blocks that are invalidated but are not yet deallocated.
  // The code GC will free them later.
  pub dead_blocks: Vec<BlockRef>,
+
+ // How many blocks were compiled when we last hit a branch stub
+ // for this ISEQ
+ pub block_count_last_stub: u64,
 }
 
 impl IseqPayload {
@@ -1908,6 +1912,7 @@ c_callable! {
 /// Called by the generated code when a branch stub is executed
 /// Triggers compilation of branches and code patching
 fn branch_stub_hit_body(branch_ptr: *const c_void, target_idx: u32, ec: EcPtr) -> *const u8 {
+ incr_counter!(branch_stub_hit);
  if get_option!(dump_insns) {
  println!("branch_stub_hit");
  }
@@ -1925,6 +1930,17 @@ fn branch_stub_hit_body(branch_ptr: *const c_void, target_idx: u32, ec: EcPtr) -
  let mut branch = branch_rc.borrow_mut();
  let branch_size_on_entry = branch.code_size();
 
+ // Compute how many blocks were compiled since the last branch stub was hit
+ let compiled_block_count = unsafe { crate::stats::COUNTERS.compiled_block_count };
+ let payload = get_iseq_payload(branch.block.borrow().blockid.iseq).unwrap();
+ let last_count = payload.block_count_last_stub;
+ let num_blocks_since = if payload.block_count_last_stub != 0 { compiled_block_count - last_count } else { 0 };
+ payload.block_count_last_stub = compiled_block_count;
+
+ if num_blocks_since > 20000 {
+ incr_counter!(branch_stub_hit_old);
+ }
+
  let target_idx: usize = target_idx.as_usize();
  let target = branch.targets[target_idx].as_ref().unwrap();
  let target_id = target.id;

yjit/src/stats.rs

@@ -327,6 +327,8 @@ make_counters! {
  defer_count,
  freed_iseq_count,
 
+ branch_stub_hit,
+ branch_stub_hit_old,
  exit_from_branch_stub,
 
  invalidation_count,