Address comments, simply to 3 levels

Author: liu-cong

docs/dev.md

@@ -21,37 +21,33 @@ The [k8s instrumentation logging guidelines](https://github.com/kubernetes/commu
 * `klog.V(4).InfoS` - Debug level verbosity
 * `klog.V(5).InfoS` - Trace level verbosity
 
-We thus define the following constants to help choosing the level:
+We choose to simplify to the following 3 common levels.
 ```
 const(
-    REQUIRED=0
-    DEFAULT_MINIMAL=1
     DEFAULT=2
     VERBOSE=3
     DEBUG=4
-    TRACE=5
 )
 ```
 
 The guidelines are written in the context of a k8s controller. Our [ext-proc](../pkg/ext-proc/) does more things such as handling requests and scraping metrics, therefore we adapt the guidelines as follows:
 
-1. The server startup process. Logging at the default verbosity level is generally welcome here as this is only logged once at startup, and provides useful info for debugging.
-   * `klog.V(REQUIRED).InfoS` = `klog.InfoS`  Default, log things such as startup flags
+1. The server startup process and configuration. 
+   * `klog.InfoS`  Logging at the `V(0)` verbosity level is generally welcome here as this is only logged once at startup, and provides useful info for debugging.
 
 2. Reconciler loops. The reconciler loops watch for CR changes such as the `InferenceModel` CR. And given changes in these CRs significantly affect the behavior of the extension, we recommend using v=1 verbosity level as default, and sparsely use higher verbosity levels.
 
-   * `klog.V(DEFAULT_MINIMAL).InfoS`
+   * `klog.V(DEFAULT).InfoS`
       * Default log level in the reconcilers.
       * Information about config (listening on X, watching Y)
       * Errors that repeat frequently that relate to conditions that can be corrected (e.g., inference model not initialized yet)
-   * `klog.V(DEFAULT).InfoS`
       * System state changing (adding/removing objects in the data store)
    * `V(VERBOSE)` and above: Use your best judgement. 
 
 3. Inference request handling. These requests are expected to be much higher volume than the control flow in the reconcilers and therefore we should be mindful of log spamming. We recommend using v=2 to log important info about a request, such as the HTTP response code, and higher verbosity levels for less important info.
 
    * `klog.V(DEFAULT).InfoS`
-      * Logging HTTP requests and their exit code
+      * Logging the status code of an HTTP request
       * Important decision making such as picking the target model, target pod
    * `klog.V(VERBOSE).InfoS`
       * Detailed request scheduling algorithm operations, such as running the filtering logic
@@ -60,8 +56,10 @@ The guidelines are written in the context of a k8s controller. Our [ext-proc](..
 4. Metric scraping loops. These loops run at a very high frequency, and logs can be very spammy if not handled properly.
     * `klog.V(DEBUG).InfoS`
       * Transient errors/warnings, such as failure to get response from a pod.
-    * `klog.V(TRACE).InfoS` - For other logs.
+      * Important state changes, such as updating a metric.
 
 5. Misc 
-   * `klog.V(VERBOSE).InfoS`
-      * A periodically (every 5s) printed debug message with the current pods and metrics. This is very important to debug the request scheduling algorithm, and yet not spammy compared to the metric scraping loop logs.
+   1. Periodic (every 5s) debug loop which prints the current pods and metrics.
+      * `klog.WarningS` If the metrics are not fresh enough, which indicates an error occurred during the metric scraping loop.
+      * `klog.V(VERBOSE).InfoS`
+         *  This is very important to debug the request scheduling algorithm, and yet not spammy compared to the metric scraping loop logs.