I use nvJPEG decode JPEG file, Why single thread and multi-thread have same speed?

Accelerated Computing GPU-Accelerated Libraries
1

Hi All,
I use nvJPEG decode JPEG file, Why single thread and multi-thread have same speed?
I use “CUDALibrarySamples/nvJPEG/nvJPEG-Decoder-MultipleInstances at master · NVIDIA/CUDALibrarySamples · GitHub” for multi thread decode test, first I use 1 thread to decode 100 images:
./build/nvJPEGDecMultipleInstances -i /data1/lishaoxiong/transcode/nv/yunshan/obs-imgs/oef-afs/src/c/data/127_1M/ -j 1 -b 1 -t 100 -w 0
image

and then I use 5 thread to decode :

image
image1349×289 73.4 KB

why 5 thread is not 5 times faster than 1 thread? they are both about 81~82 seconds