我一直在使用它：
os.environ["CUDA_VISIBLE_DEVICES"] = "1"
以便在GPU上运行。从今天开始，它一直在正常工作。
现在的问题是，在运行时的中间，我的程序停止使用GPU并切换到CPU，因此它变得太慢了。
为什么会这样？
开始执行nvidia-smi时的输出：
+-----------------------------------------------------------------------------+
| NVIDIA-SMI 418.67 Driver Version: 418.67 CUDA Version: 10.1 |
|-------------------------------+----------------------+----------------------+
| GPU Name Persistence-M| Bus-Id Disp.A | Volatile Uncorr. ECC |
| Fan Temp Perf Pwr:Usage/Cap| Memory-Usage | GPU-Util Compute M. |
|===============================+======================+======================|
| 0 GeForce GTX 970 On | 00000000:01:00.0 On | N/A |
| 0% 42C P8 14W / 200W | 363MiB / 4039MiB | 0% Default |
+-------------------------------+----------------------+----------------------+
| 1 Tesla K40c On | 00000000:05:00.0 Off | 0 |
| 35% 74C P0 136W / 235W | 11011MiB / 11441MiB | 94% Default |
+-------------------------------+----------------------+----------------------+
+-----------------------------------------------------------------------------+
| Processes: GPU Memory |
| GPU PID Type Process name Usage |
|=============================================================================|
| 0 1037 G /usr/lib/xorg/Xorg 20MiB |
| 0 1150 G /usr/bin/gnome-shell 12MiB |
| 0 7430 G /usr/lib/xorg/Xorg 166MiB |
| 0 7560 G /usr/bin/gnome-shell 158MiB |
| 1 13772 C python3 10998MiB |
+-----------------------------------------------------------------------------+
然后，当它开始运行太慢时：
+-----------------------------------------------------------------------------+
| NVIDIA-SMI 418.67 Driver Version: 418.67 CUDA Version: 10.1 |
|-------------------------------+----------------------+----------------------+
| GPU Name Persistence-M| Bus-Id Disp.A | Volatile Uncorr. ECC |
| Fan Temp Perf Pwr:Usage/Cap| Memory-Usage | GPU-Util Compute M. |
|===============================+======================+======================|
| 0 GeForce GTX 970 On | 00000000:01:00.0 On | N/A |
| 0% 42C P8 14W / 200W | 363MiB / 4039MiB | 0% Default |
+-------------------------------+----------------------+----------------------+
| 1 Tesla K40c On | 00000000:05:00.0 Off | 0 |
| 35% 69C P0 63W / 235W | 11011MiB / 11441MiB | 0% Default |
+-------------------------------+----------------------+----------------------+
+-----------------------------------------------------------------------------+
| Processes: GPU Memory |
| GPU PID Type Process name Usage |
|=============================================================================|
| 0 1037 G /usr/lib/xorg/Xorg 20MiB |
| 0 1150 G /usr/bin/gnome-shell 12MiB |
| 0 7430 G /usr/lib/xorg/Xorg 166MiB |
| 0 7560 G /usr/bin/gnome-shell 158MiB |
| 1 13772 C python3 10998MiB |
+-----------------------------------------------------------------------------+