[tidbx] tidb cpu and workload latency jitter when RCU reaches the threshold

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)
1，create cluster with RCU Max: 60000
2，run sysbench
sysbench /usr/share/sysbench/oltp_read_write.lua \
--mysql-host='' \
--mysql-port=4000 \
--mysql-user='root' \
--mysql-password='***REDACTED***' \
--mysql-db='test' \
--tables=2 \
--table-size=2500000000 \
--threads=64 \
--time=1800 \
--report-interval=10 \
--percentile=95 \
--rand-type=uniform \
run

### 2. What did you expect to see? (Required)
cpu and latency should not jitter

### 3. What did you see instead (Required)
RCU reached MAX 60000，tidb cpu and workload latency jitter

### 4. What is your TiDB version? (Required)