Revise TSO related Grafana monitoring metrics description (pingcap#18722)

Author: lilin90

dashboard/dashboard-monitoring.md

@@ -69,11 +69,11 @@ Number of queries using plan cache per second in all TiDB instances
 ### KV/TSO Request OPS
 
 - kv request total: Total number of KV requests per second in all TiDB instances
-- kv request by type: Number of KV requests per second in all TiDB instances based on such types as `Get`, `Prewrite`, and `Commit`.
-- tso - cmd: Number of `tso cmd` requests per second in all TiDB instances
-- tso - request: Number of `tso request` requests per second in all TiDB instances
+- kv request by type: Number of KV requests per second in all TiDB instances based on such types as `Get`, `Prewrite`, and `Commit`
+- tso - cmd: Number of gRPC requests per second that TiDB sends to PD in all TiDB instances; each gRPC request contains a batch of TSO requests
+- tso - request: Number of TSO requests per second in all TiDB instances
 
-Generally, dividing `tso - cmd` by `tso - request` yields the average batch size of requests per second.
+Generally, `tso - request` divided by `tso - cmd` is the average size of TSO request batches per second.
 
 ### Connection Count
 

grafana-overview-dashboard.md

@@ -42,7 +42,7 @@ To understand the key metrics displayed on the Overview dashboard, check the fol
 | TiDB | Transaction Duration | The execution time of a transaction |
 | TiDB | KV Cmd OPS | The number of executed KV commands. |
 | TiDB | KV Cmd Duration 99 | The execution time of the KV command. |
-| TiDB | PD TSO OPS | The number of TSO that TiDB obtains from PD per second. |
+| TiDB | PD TSO OPS | The number of gRPC requests per second that TiDB sends to PD (cmd) and the number of TSO requests (request); each gRPC request contains a batch of TSO requests. |
 | TiDB | PD TSO Wait Duration | The duration that TiDB waits for PD to return TSO. |
 | TiDB | TiClient Region Error OPS | The number of Region related errors returned by TiKV. |
 | TiDB | Lock Resolve OPS | The number of TiDB operations that resolve locks. When TiDB's read or write request encounters a lock, it tries to resolve the lock. |

grafana-performance-overview-dashboard.md

@@ -67,11 +67,11 @@ Number of commands processed by all TiDB instances per second based on type
 ### KV/TSO Request OPS
 
 - kv request total: Total number of KV requests per second in all TiDB instances
-- kv request by type: Number of KV requests per second in all TiDB instances based on such types as `Get`, `Prewrite`, and `Commit`.
-- tso - cmd: Number of `tso cmd` requests per second in all TiDB instances
-- tso - request: Number of `tso request` requests per second in all TiDB instances
+- kv request by type: Number of KV requests per second in all TiDB instances based on such types as `Get`, `Prewrite`, and `Commit`
+- tso - cmd: Number of gRPC requests per second that TiDB sends to PD in all TiDB instances; each gRPC request contains a batch of TSO requests
+- tso - request: Number of TSO requests per second in all TiDB instances
 
-Generally, dividing `tso - cmd` by `tso - request` yields the average batch size of requests per second.
+Generally, `tso - request` divided by `tso - cmd` is the average size of TSO request batches per second.
 
 ### KV Request Time By Source
 
@@ -138,10 +138,10 @@ Average time consumed in executing gRPC requests in all TiKV instances based on
 
 ### PD TSO Wait/RPC Duration
 
-- wait - avg: Average time in waiting for PD to return TSO in all TiDB instances
-- rpc - avg: Average time from sending TSO requests to PD to receiving TSO in all TiDB instances
-- wait - 99: P99 time in waiting for PD to return TSO in all TiDB instances
-- rpc - 99: P99 time from sending TSO requests to PD to receiving TSO in all TiDB instances
+- wait - avg: Average duration of waiting for PD to return TSO in all TiDB instances
+- rpc - avg: Average duration from the time that TiDB sends gRPC requests to PD to get TSO to the time that TiDB receives TSO in all TiDB instances
+- wait - 99: P99 duration of waiting for PD to return TSO in all TiDB instances
+- rpc - 99: P99 duration from the time that TiDB sends gRPC requests to PD to get TSO to the time that TiDB receives TSO in all TiDB instances
 
 ### Storage Async Write Duration, Store Duration, and Apply Duration
 

grafana-tidb-dashboard.md

@@ -133,10 +133,10 @@ The following metrics relate to requests sent to TiKV. Retry requests are counte
 - PD Client CMD OPS: the statistics of commands executed by PD Client per second
 - PD Client CMD Duration: the time it takes for PD Client to execute commands
 - PD Client CMD Fail OPS: the statistics of failed commands executed by PD Client per second
-- PD TSO OPS: the number of TSO that TiDB obtains from PD per second
+- PD TSO OPS: the number of gRPC requests per second that TiDB sends to PD (cmd) and the number of TSO requests (request); each gRPC request contains a batch of TSO requests
 - PD TSO Wait Duration: the time that TiDB waits for PD to return TSO
-- PD TSO RPC duration: the duration from the time that TiDB sends request to PD (to get TSO) to the time that TiDB receives TSO
-- Start TSO Wait Duration: the duration from the time that TiDB sends request to PD (to get `start TSO`) to the time that TiDB receives `start TSO`
+- PD TSO RPC duration: the duration from the time that TiDB sends gRPC requests to PD to get TSO to the time that TiDB receives the gRPC response from PD
+- Async TSO Duration: the duration from the time that TiDB prepares to get TSO to the time that TiDB actually starts to wait for PD to return TSO
 
 ### Schema Load