Tensorboard shows huge idle time and no blank spaces on GPU
Hi @alex19999, 
In order to expedite the trouble-shooting process, kindly share complete reproducible code to replicate the issue reported here. Thank you! This issue has been automatically marked as stale because it has no recent activity. It will be closed if no further activity occurs. Thank you.
 Closing as stale. Please reopen if you'd like to work on this further.
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<details><summary>Click to expand!</summary> 
 
 ### Issue Type

Bug

### Have you reproduced the bug with TF nightly?

Yes

### Source

source

### Tensorflow Version

tf. 2.9

### Custom Code

Yes

### OS Platform and Distribution

Linux Ubuntu 20.04

### Mobile device

Linux Ubuntu 20.04

### Python version

3.9

### Bazel version

_No response_

### GCC/Compiler version

_No response_

### CUDA/cuDNN version

11.3

### GPU model and memory

Nvidia GeForce RTX 3090

### Current Behaviour?

```shell
I'm new to TF profiler and tensorboard. Could you please tell me how GPU idle time is calculated? I see contradictory data in profiling information on tensorboard and no information about it in docs:

 - I have no blank spaces in events trace (GPU compute stream) presented on `trace_viewer` page.
 - Wherein device (GPU) idle time shown on `tensorflow_stats` page is about 50%???

It's what I see when I use small batch size. After increasing batch size, same situation is on `trace_viewer` page, but GPU idle time decreased up to 7%. So, how is idle time calculated?

By the way, another two questions:
1. What is `steps` on `trace_viewer` page?
2. Why does `trace_viewer` page contain only a part of profiling time? I profiled about 100 seconds of execution, but I see only 10 seconds on `trace_viewer` page.


Thanks a lot in advance!
```


### Standalone code to reproduce the issue

```shell
I've used next setup:
tf.profiler.experimental.start
<training>
tf.profiler.experimental.end
```


### Relevant log output

_No response_</details>