fread in faster in testChunkEngine

Hi, In testChunkEngine.cc，I run the code in the linux server, fread shows a better performance, while I thought given the conclusion from 3FS. AIO should provide a better performance. I also tried tuning the parameters, but the result is the same.
So is there any examples to illustrate that AIO could perform better performance than fread?

`
Creating test file...
Running benchmarks...
fread: 6972.07 MB/s
AIO: 455.35 MB/s
`

Start with testChunkEngine.cc and reproduce the reported Linux benchmark comparing fread at 6972.07 MB/s with AIO at 455.35 MB/s. Trace the two benchmark paths and their tunable parameters, then verify the comparison under the same conditions; done means the performance difference is explained and an AIO example or confirmed limitation is documented.

Written by the indexing model from the issue text.