Add squashing metrics (#3573)

core/src/bank_forks.rs

@@ -1,9 +1,12 @@
 //! The `bank_forks` module implments BankForks a DAG of checkpointed Banks
 
 use hashbrown::{HashMap, HashSet};
+use solana_metrics::counter::Counter;
 use solana_runtime::bank::Bank;
+use solana_sdk::timing;
 use std::ops::Index;
 use std::sync::Arc;
+use std::time::Instant;
 
 pub struct BankForks {
     banks: HashMap<u64, Arc<Bank>>,
@@ -99,12 +102,17 @@ impl BankForks {
     }
 
     pub fn set_root(&mut self, root: u64) {
+        let set_root_start = Instant::now();
         let root_bank = self
             .banks
             .get(&root)
             .expect("root bank didn't exist in bank_forks");
         root_bank.squash();
         self.prune_non_root(root);
+        inc_new_counter_info!(
+            "bank-forks_set_root_ms",
+            timing::duration_as_ms(&set_root_start.elapsed()) as usize
+        );
     }
 
     fn prune_non_root(&mut self, root: u64) {