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Old 2018-12-24, 22:06   #3
kriesel's Avatar
Mar 2017
US midwest

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Default Prime95 P-1 run time scaling

A small number of widely spaced exponents were run to observe the run time scaling.

For prime95 v29.4b8 x64 run on a Windows 7 x64 system with dual e5-2670 chips, 4 cores (half a chip package) per worker, 32,000 MB allowance per worker, run time was approximately proportional to exponent p2.33 up to 595M (27 days), a somewhat higher power than observed for P-1 on gpus (~2.1).

Another prime95 v29.4b8 x64 run on an FMA equipped i7-7500U Windows 10 X64 system seemed to be taking inordinately long to perform P-1, at p=101M, on 7,200 MB memory allowed, one core. It had been running for two weeks to perform stage 1 and reach 90% in stage 2. It appeared to be paging to disk excessively. The same system can complete an 83M primality test per core in about 2.5 weeks. It was allowed to complete that P-1 and then reset to 4096M memory allowed, after it was found to still page excessively at 6144M. This is a system with 8GB ram currently. In all cases it was running 1 core per worker; the other worker was running an 83M LL. It projected P-1 run times ranging from 4.4 days for 201M to 43 days for 605M, 67 days for 701M. However, attempting 605M resulted in "Cannot initialize FFT code, errcode=1002".
The fit to observed run time is p2.087 (with five data points).

Another run, a mix of prime95 V29.7b1, v29.8b3, and v29.8b6, on an FMA equipped i7-8750H Windows 10 X64 system was able to run 801M (at 8GB allocated of its 16GB installed ram, 37 days run time), and 901M (at 12GB allocated, 57 days run time) and is expected to be capable of up to 920.8M. The offset in the estimated days runtime is believed to be due to whether mfakto is running on the Intel igp or not. It seems to be using somewhat lower bounds than GPU72 figures for exponents above p~400M.

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Attached Files
File Type: pdf p-1 run time scaling e5-2670.pdf (14.1 KB, 191 views)
File Type: pdf p-1 run time scaling FMA i7-7500u.pdf (16.1 KB, 195 views)
File Type: pdf p-1 run time scaling FMA i7-8750H.pdf (18.4 KB, 195 views)

Last fiddled with by kriesel on 2020-01-05 at 14:05 Reason: updated i7-8750h attachment for new data
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