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Fails to save arrays > 4GB
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Joined: 10 Mar 2008
Posts: 2777
Location: South Pole, Antarctica

PostPosted: Wed Jul 26, 2023 9:15 pm    Post subject: Re: Reply with quote

JohnCampbell wrote:

Write OK. Speed of write Method 1 = 0.360 0.359 GB/sec
READ OK. Speed of read Method 1 = 0.462 0.455 GB/sec

Huge improvement on your new method vs old method, 0.360 vs 0.359, right ?
What numbers i was interested to see asking Paul to repeat the test? Method1 because they show 2x improvement versus mine

Why i asked this? Because there are couple major differences between his PC and mine PC: processor type and DDR4 vs DDR5 type of memory. I never seen 2x differences with the same generation processors and no matter how fast memory i used i never got more than 10-20% differences before. If some specific processor/memory type combination plays such huge difference that could potentially improve my numerical simulations speed 2x if i switch. So with Method 1 I was actually not interested with the speed of harddrive (i will use for that Method2) but the speed of some other computer sybsystem this test abruptly revealed

Why i was not interested with your "improvements"? Because my Method 1 runs for a long time and there will be no differences between any timers. Method 2 is much faster but it will be stopped by the speed of PCIe/drive speed itself anyway and i also need it to read/write only huge files where test runs for a long time.

If you are interested with general timer improvement try to convince Silverfrost to create new timer. Though FTN95 needs other much more important things to improve to be a compiler of 21th century. But when something needs the improvements here you quietly vote with your feet for other compilers where all that things are already realized
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Joined: 16 Feb 2006
Posts: 2506
Location: Sydney

PostPosted: Thu Jul 27, 2023 4:19 am    Post subject: Reply with quote


I don't think it is too difficult to understand the difference between elapsed time and CPU allocated time.
Clearly the difference is more significant with Method 2, where there are more disk wait delays.

In my previous results I linked in Posted: Fri Jul 21, 2023 8:42 pm, I tried to in better identify this problem, by also reporting % CPU usage as a proportion of elapsed time.

============ Trying to save the data Method 2 ============
Method 2 write  6.7683 el  2.9687 cp    43.86 %
Write OK.  Speed of write  Method 2=   2.964   1.300 GB/sec

============ Now read Method 2 ============
Method 2 read   2.0316 el  1.6719 cp    82.29 %
READ OK. Speed of read   Method 2 =   5.264   4.332 GB/sec

In my most recent post I tried to explain the many reasons why there are problems with testing IO performance and also explain how the use of CPU_TIME significantly overestimated the Method 2 performance.

Because there is a lot more CPU usage for Method 1, the alternative rate estimates are not so inconsistent, which I expected you would have understood.

The only improvement for FTN95 would be to provide an integer*8 function rdtsc_ticks () ( and integer*8 function rdtsc_tick_rate () ), although this is not required for these tests. This should be provided by all compilers !
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