Credit notes

Some random notes about credit.

Inconsistent goals

Consider these goals:

• Project neutrality: a given host should get the same credit/day from any project.
• Device neutrality: a given job should get the same credit on different hosts.

Consider the following scenario:

• Two projects and two hosts
• Host A runs both projects' jobs in 1 hour.
• Host B runs project 1's jobs in 1 hour, and project 2's job in 10 hours.

Project neutrality says that both projects must grant host A the same credit per job. Then device neutrality says that both projects must grant host B the same credit per job. But that violates project neutrality for host B.

So the two goals are inconsistent; we can't satisfy them both.

Scenarios

Extending the above example: suppose

• the 2 hosts both have the same peak FP speed (say 1 GFLOPS).
• project 1's app runs with 100% efficiency on both hosts
• project 2's app runs with 100% efficiency on host A and 10% efficiency on host B (say, because of its memory access pattern)