AcctIdx: stats for how much time bg threads wait (#20127)

runtime/src/bucket_map_holder.rs

@@ -3,6 +3,7 @@ use crate::bucket_map_holder_stats::BucketMapHolderStats;
 use crate::in_mem_accounts_index::{InMemAccountsIndex, SlotT};
 use crate::waitable_condvar::WaitableCondvar;
 use solana_bucket_map::bucket_map::{BucketMap, BucketMapConfig};
+use solana_measure::measure::Measure;
 use solana_sdk::clock::SLOT_MS;
 use solana_sdk::timing::AtomicInterval;
 use std::fmt::Debug;
@@ -157,9 +158,15 @@ impl<T: IndexValue> BucketMapHolder<T> {
         let bins = in_mem.len();
         let flush = self.disk.is_some();
         loop {
+            let mut m = Measure::start("wait");
             // this will transition to waits and thread throttling
             self.wait_dirty_or_aged
                 .wait_timeout(Duration::from_millis(AGE_MS));
+            m.stop();
+            self.stats
+                .bg_waiting_us
+                .fetch_add(m.as_us(), Ordering::Relaxed);
+
             if exit.load(Ordering::Relaxed) {
                 break;
             }

runtime/src/bucket_map_holder_stats.rs

@@ -24,6 +24,7 @@ pub struct BucketMapHolderStats {
     pub deletes: AtomicU64,
     pub inserts: AtomicU64,
     pub count: AtomicU64,
+    pub bg_waiting_us: AtomicU64,
     pub count_in_mem: AtomicU64,
     pub per_bucket_count: Vec<AtomicU64>,
     pub flush_entries_updated_on_disk: AtomicU64,
@@ -119,6 +120,11 @@ impl BucketMapHolderStats {
                 i64
             ),
             ("count", self.count.load(Ordering::Relaxed), i64),
+            (
+                "bg_waiting_us",
+                self.bg_waiting_us.swap(0, Ordering::Relaxed),
+                i64
+            ),
             ("min_in_bin", min, i64),
             ("max_in_bin", max, i64),
             ("count_from_bins", ct, i64),