Message boards : ATLAS application : Hyperthreading/SMT
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Message 34403 - Posted: 19 Feb 2018, 4:29:39 UTC

Just wondering if there is any noticeable difference between running hyperthreading/smt on or off?

Lets say a user has lots of cores/threads but limited ram. (Less than 2GB per core)

Would it be worth it (points wise) to disable hyperthreading?

Has anyone had any experience testing this? (I probably will...but thought I'd save some time)

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Crystal Pellet
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Message 34406 - Posted: 19 Feb 2018, 8:19:16 UTC - in response to Message 34403.  

I did not test with HT on/off, but with running a 4-core ATLAS VM with and without the other 4 threads idle.

With half of my 8 threads idle the ATLAS job finished much faster.
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David Cameron
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Message 34407 - Posted: 19 Feb 2018, 10:35:53 UTC - in response to Message 34406.  

I posted about this a long time ago but it was probably in the old ATLAS project forums.

I have a 4+4HT machine and found I got the same work done running 1 4 core WU as 1 8-core WU, i.e. the 8-core WU are twice as slow but have twice as many threads so finish in the same time.

I think this is because virtualbox is not so good at exploiting HT - I have not done the same test with the native Linux version but it might work better with HT.
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Message 34412 - Posted: 19 Feb 2018, 11:11:56 UTC

One Horse have only ONE HorsePower ;-))
T4T shows a Benchmark in the log.
2018-02-18 16:44:04 (3348): Guest Log: [INFO] Running the fast benchmark.
2018-02-18 16:45:32 (3348): Guest Log: [INFO] Machine performance 6.01 HEPSEC06

The combination of CPU, RAM, Disk(SSD) is so difficult, that there is no perfect solution for every Computer.
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Message boards : ATLAS application : Hyperthreading/SMT

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