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Old 2022-07-25, 10:34   #1
Th3D0kt0r
 
Jul 2022

210 Posts
Default Optimising for Azure F-series

Hi all - I'm quite new to the GIMPS project, but am really enjoying being involved :-)


I have access to a few Azure subscriptions, so I thought I'd spin up a couple of VMs and try get mprime working. I've provisioned an Ubuntu VM using an F2s_v2, which has 2 x vCPUS (Intel(R) Xeon(R) Platinum 8272CL CPU @ 2.60GHz) and 4GB RAM:


https://docs.microsoft.com/en-us/azu...es/fsv2-series


The CPUs are Cascade Lake, but the performance of the current work assignment (LL Double-check) is surprisingly slow. The current exponent will take around 13 days to complete, but a similar job on my old 4-core i7 laptop only took around 5 days. I'm guessing that either I haven't optimised things properly, or I just don't get how it's meant to be working.


CPU utilisation seems to be capped out at 50%, so there's definitely extra performance to be had.


This is the output of lscpu:


Code:
Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
Address sizes: 46 bits physical, 48 bits virtual
CPU(s): 2
On-line CPU(s) list: 0,1
Thread(s) per core: 2
Core(s) per socket: 1
Socket(s): 1
NUMA node(s): 1
Vendor ID: GenuineIntel
CPU family: 6
Model: 85
Model name: Intel(R) Xeon(R) Platinum 8272CL CPU @ 2.60GHz
Stepping: 7
CPU MHz: 2593.907
BogoMIPS: 5187.81
Virtualization: VT-x
Hypervisor vendor: Microsoft
Virtualization type: full
L1d cache: 32 KiB
L1i cache: 32 KiB
L2 cache: 1 MiB
L3 cache: 35.8 MiB
NUMA node0 CPU(s): 0,1
Has anyone else had any experience with Cascade Lake processors or thoughts on how to troubleshoot? Any assistance gratefully received :-)
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Old 2022-07-25, 14:30   #2
axn
 
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Sounds about right. Single core 13 days vs 4 core 5 days sounds pretty good.
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Old 2022-07-25, 14:46   #3
kriesel
 
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"TF79LL86GIMPS96gpu17"
Mar 2017
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Quote:
Originally Posted by Th3D0kt0r View Post
CPU utilisation seems to be capped out at 50%, so there's definitely extra performance to be had.

This is the output of lscpu:
Code:
Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
Address sizes: 46 bits physical, 48 bits virtual
CPU(s): 2
On-line CPU(s) list: 0,1
Thread(s) per core: 2
Core(s) per socket: 1
Socket(s): 1
That's one core, both hyperthreads. 50% of 2 hyperthreads is one thread. It's maxed out. That's same as Colab free; 1 core 2 hyperthreads. Mprime typically does not benefit from running dual hyperthreads on a core for fft-based computations such as LL. It is typically memory bound, so much so George trades more instructions to reduce memory bandwidth requirements per fft iteration.

Last fiddled with by kriesel on 2022-07-25 at 14:52
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Old 2022-07-25, 21:17   #4
Th3D0kt0r
 
Jul 2022

2 Posts
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Quote:
Originally Posted by kriesel View Post
That's one core, both hyperthreads. 50% of 2 hyperthreads is one thread. It's maxed out. That's same as Colab free; 1 core 2 hyperthreads. Mprime typically does not benefit from running dual hyperthreads on a core for fft-based computations such as LL. It is typically memory bound, so much so George trades more instructions to reduce memory bandwidth requirements per fft iteration.

Thanks for the info. Does that mean that there's not much difference in provisioning a single core VM (F1s_v2) vs a two-core system? I'm just thinking that I could spin up two VMs for the price of one, if that's the case.


Additionally, what's the recommendation with regards to configuration of memory usage? The current VM has 4GB RAM, but mprime is only using about 300MB. There's nothing else running on the system, so it can certainly go higher. I have tried tweaking the memory usage in prime95 on a Windows box, but even with restarting the app it never seems to try and use what I've made available.
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