Speedup

In computer architecture, speedup is a number that measures the relative performance of two systems processing the same problem. More technically, it is the improvement in speed of execution of a task executed on two similar architectures with different resources. The notion of speedup was established by Amdahl's law, which was particularly focused on parallel processing. However, speedup can be used more generally to show the effect on performance after any resource enhancement.

Definitions

Speedup can be defined for two different types of quantities: latency and throughput.

Latency of an architecture is the reciprocal of the execution speed of a task:

L

=

1

v

=

T

W

,

{\displaystyle L={\frac {1}{v}}={\frac {T}{W}},}

where

v is the execution speed of the task;

T is the execution time of the task;

W is the execution workload of the task.

Throughput of an architecture is the execution rate of a task:

Q

=

ρ

v

A

=

ρ

A

W

T

=

ρ

A

L

,

{\displaystyle Q=\rho vA={\frac {\rho AW}{T}}={\frac {\rho A}{L}},}

where

ρ is the execution density (e.g., the number of stages in an instruction pipeline for a pipelined architecture);

A is the execution capacity (e.g., the number of processors for a parallel architecture).

Latency is often measured in seconds per unit of execution workload. Throughput is often measured in units of execution workload per second. Another unit of throughput is instructions per cycle (IPC) and its reciprocal, cycles per instruction (CPI), is another unit of latency.