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Old 2020-03-25, 16:59   #793
kladner
 
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Quote:
Originally Posted by Viliam Furik View Post
Could you do it on range of FFTs (e.g. 2048 to 8192), and without testing all implementations?
It will take a little while, but under lockdown I have time on my hands.
EDIT: Here ya go.
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File Type: txt CPU clock bench 02.txt (9.6 KB, 12 views)

Last fiddled with by kladner on 2020-03-25 at 17:49
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Old 2020-03-25, 21:18   #794
Viliam Furik
 
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Quote:
Originally Posted by kladner View Post
It will take a little while, but under lockdown I have time on my hands.
EDIT: Here ya go.
Thank you. I've looked at the results, and it seems like there is little advantage from RAM speed with those speeds and that CPU. And for some reason, the 4000 turns out fastest on some FFT lengths, but it is not that much so it may be a measurement error (some background tasks).

Is it possible that when RAM is faster than CPU clock, it will not be used the same as with faster CPU? I'm thinking about this exact thing, because I have 3200 MHz RAM now, and I want to know whether I should buy 4000 MHz or 4400 MHz RAM because my CPU is manually overclocked to 4,1 GHz (Ryzen 9 3900X).
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Old 2020-03-25, 22:02   #795
Prime95
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Quote:
Originally Posted by Viliam Furik View Post
Thank you. I've looked at the results, and it seems like there is little advantage from RAM speed with those speeds and that CPU.
Note the massive L3 cache on that chip. It is not surprising that RAM speed is not a factor.
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Old 2020-03-26, 01:51   #796
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Quote:
Originally Posted by Prime95 View Post
Note the massive L3 cache on that chip. It is not surprising that RAM speed is not a factor.
L3 is 8MB on a 6700K, which is mediocre.
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Old 2020-03-26, 02:25   #797
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I think he was referring to the Ryzen?
Edit: 70MB L3, if my search result is to be believed.

Last fiddled with by VBCurtis on 2020-03-26 at 02:26
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Old 2020-03-26, 03:04   #798
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Quote:
Originally Posted by axn View Post
L3 is 8MB on a 6700K, which is mediocre.
Sorry, confused the benchmark with JCoveiro's Ryzen.
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Old 2020-03-26, 03:40   #799
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Quote:
Originally Posted by Prime95 View Post
Sorry, confused the benchmark with JCoveiro's Ryzen.
Ok, makes sense. That still leaves the question of why mem speed is not affecting performance. I suppose, with just 4 cores, all of the tested RAM speeds are sufficient to feed the CPU.

Quote:
Originally Posted by VBCurtis View Post
I think he was referring to the Ryzen?
Edit: 70MB L3, if my search result is to be believed.
Ryzen L3 are all power-of-2, but since it is a victim cache, AMD specs list L2+L3 as a single "cache" number. So if you see 70MB for a processor, that is 64MB L3 + 6MB (12*512KB) L2.
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Old 2020-03-26, 16:15   #800
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I have to note that the RAM speed was the same in all these runs. Only the CPU clock was different. I took the very similar results as an indication that this system is memory-bound.
EDIT: Also, these tests were not run under strict lab-like conditions. I did shut down obvious cycle-stealing apps like performance monitors and browsers. In line with normal operation on the machine I deliberately left mfaktc running on the GPU as part of the environment. Allowance has to be made for margin-of-error.

Last fiddled with by kladner on 2020-03-26 at 16:21
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