TiDB v5.1.0 consumes more CPU than v5.0.2 in ycsb workload-e

[youjiali1995]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

Topo:

          spec:
            machines:
              - name: m1
                exclusive: true
            items:
              - name: tidb
                spec:
                  memory: 32GB
                  cores: 16
                  machine: m1
              - name: pd
                spec:
                  memory: 8GB
                  cores: 2
                  machine: m1
              - name: tikv-1
                spec:
                  memory: 64GB
                  cores: 16
                  disks:
                    disk1:
                      kind: nvme
                      mountPath: /disk1
                  machine: m1
              - name: workload
                spec:
                  memory: 8GB
                  cores: 4
                  machine: m1

ycsb workload-e:

                      echo "recordcount=100000000" >> global.conf
                      echo "operationcount=10000000" >> global.conf
                      echo "workload=core" >> global.conf
                      echo "fieldcount=10" >> global.conf
                      echo "fieldlength=100" >> global.conf
                      echo "threadcount=500" >> global.conf
                      echo "requestdistribution=zipfian" >> global.conf
                      go-ycsb run mysql \
                          -P /ycsb/workloads/{{workflow.parameters.workload}} \
                          -P global.conf \
                          -p mysql.host=$tidb \
                          -p mysql.port=4000

2. What did you expect to see? (Required)

Same throughput and CPU usage.

3. What did you see instead (Required)

The throughput is the same(?) in the two versions but CPU usage is different.

v5.1

v5.0.2

4. What is your TiDB version? (Required)

v5.1.0 go1.16.4
v5.0.2 go1.13

[youjiali1995]

/cc @sticnarf

[youjiali1995]

BTW, the ycsb workload-e is a TiDB CPU-bound workload. I guess there are many potiential optimizations here.

Related to #25573 (comment).