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Old 2022-09-27, 14:29   #1
maxal
 
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Default msieve claims to use 32 threads but uses only 16

I've noticed that while msieve 1.54 claims commencing Lanczos iteration (32 threads), in reality it uses only 16 threads (as system monitoring shows). What could be wrong?

Last fiddled with by maxal on 2022-09-27 at 14:35
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Old 2022-09-27, 14:40   #2
Uncwilly
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Are you looking at the cores being used? Is it possible that the Intel hyperthreading is involved? That could explain the difference.
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Old 2022-09-27, 15:30   #3
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Quote:
Originally Posted by Uncwilly View Post
Are you looking at the cores being used? Is it possible that the Intel hyperthreading is involved? That could explain the difference.
Not really. I have 20 cores, 2 threads per core, and so 40 (hyper)threads overall. Msieve utilizes only 16 threads while the other 24 are idling.

Last fiddled with by maxal on 2022-09-27 at 15:34
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Old 2022-09-27, 16:54   #4
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The sparse matrix-vector product (SpMV) is memory bound. The idle threads are waiting for data.
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Old 2022-09-28, 02:18   #5
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Quote:
Originally Posted by frmky View Post
The sparse matrix-vector product (SpMV) is memory bound. The idle threads are waiting for data.
Then in my case they are waiting forever as the load never goes above 16 threads.
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