PPPA_pdes (1158465), страница 2

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This is the ratio of effective time to the product of number of processors by execution time.

1. The lost time T_{Lost_time}.

T_{Lost_time} = N * T_{Total_execution_time} - T_{Sequential_execution_time}

It is a difference between product of number of processors by execution time and effective time. The lost time is represented as the sum of the following components:

• Time losses due to replicated calculations (at execution of one branch by several processors) is the sum of times of replicated calculations of all processors except input-output processor.

• Waiting time of a reduction is the sum of the corresponding times on all processors.

• Waiting time of updating of shadow edges is the sum of the corresponding times on all processors.

• Waiting time of moving of data during redistribution of arrays - sum of the corresponding times on all processors.

• Time of loading of buffers for access to the remote elements of the distributed arrays - sum of the corresponding times on all processors.

• Time of message exchange during execution of functions of exchange with files - sum of the message times on all processors.

• The time of imbalance of processor load s - the maximal value from the times of execution on all processors is calculated and then the deviations of the execution time on each processor from this maximal value are summed up.

For the reduction waiting time and updating of shadow edges waiting time dissynchronization times are also calculated. These times are calculated by summation of the corresponding dissynchronization times for each processor, calculated by the formulas given in the previous section. .

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