That depends on the description of your problem, but there is one for the heterogenous computing scheduling problem (HCSP) 

https://www.fing.edu.uy/inco/grupos/cecal/hpc/HCSP/HCSP_inst.htm

A smallest of instances from diverse authors can be found here:

http://ieeexplore.ieee.org/document/6681301/?arnumber=6681301

Another definition of scheduling problem in cloud computing: 

http://link.springer.com/article/10.1007%2Fs10723-015-9337-8

Dear Jose Carlos, Thanks for your kind response. I downloaded the instances files from the first URL. Is it the sizes of tasks?

You may also look at the Google Cluster Dataset. It contains all information of the jobs submitted to the cluster. 

Can i get google cluster dataset as i tried a lot but could not find it to download?

You can download the Google cluster dataset from its repository here.

https://github.com/google/cluster-data

Thanks Sir, if i am trying it, if faced any problem, then i will take your guidance please...

Dear Sir Tram Truong-Huu,

I have downlaoded google-cluster-data-1, but it did not have the size of jobs? I need the size of jobs and the ratio of smaller and larger jobs what i should use in my dataset for job scheduling on cloud computing. I would be thankful if got your further guidance please...

I believe you need to adopt the Google dataset to your needs as the definition of job size may be different from different point of views (volume of input data, execution time of job...) . Please check what are available in the Google dataset and convert it according to your definition. 

can you help me too find data set of task scheduling

Kindly read my article "GoCJ: Google Cloud Jobs dataset for Distributed and Cloud infrastructure."