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Old 2021-04-20, 18:06   #23
bur
 
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SSH is installed and works, I used it from the same machine I now accessed via Teamviewer, so very likely it's a power saving issue. Thanks for the help.


I'm really looking forward to this, finally I can also try cado-nfs. So ... being so very enthusiastic about running factorization programs in a terminal sounds a bit weird, but other than consuming energy at least it's a hobby that hurts no one. ;)

Last fiddled with by bur on 2021-04-20 at 18:10
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Old 2021-04-20, 18:32   #24
chalsall
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Quote:
Originally Posted by bur View Post
So ... being so very enthusiastic about running factorization programs in a terminal sounds a bit weird, but other than consuming energy at least it's a hobby that hurts no one. ;)
Careful! It can become a bit addictive... I'm currently doing TF and P-1'ing in 23 or so different consoles spread across dozens of real and VMs controlled by about a half dozen GUI environments in virtual, local and remotely accessed machines...
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Old 2021-04-21, 07:56   #25
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Everything seems to work now, but Dell apparently doesn't build their system for 100% CPU utilization... CPU fan goes berserk and it still reaches 86 °C and up all the time.

So far I limited long term power to 80 W (from 125 W) which made the temperature go down to a steady 73 °C, but it's not ideal of course. So now I'll have to see if I can fit a good cooler inside that small case or if I'll be forced to take everything apart and rebuild it in a new case.

chalsall, quite true.
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Old 2021-04-21, 08:04   #26
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Quote:
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... reaches 86 °C and up all the time.
86C is fine for silicon.

Anything up to 95C is okay IME.
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Old 2021-04-21, 08:13   #27
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Ok, good to know. But since it even went beyond 90 °C a few times I'm worried it might exceed 95 °C especially in the (hopefully) warmer days to come.

I'll see what type of cooler I can fit and then decide how to proceed.
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Old 2021-04-21, 08:33   #28
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Quote:
Originally Posted by bur View Post
Ok, good to know. But since it even went beyond 90 °C a few times I'm worried it might exceed 95 °C especially in the (hopefully) warmer days to come.

I'll see what type of cooler I can fit and then decide how to proceed.
It should reduce the clock speed if it hits 95C. I don't think you need to worry about it hitting 95C. That said I don't think I would leave it there.
It does feel like the temperature difference is too high. Something is going wrong beyond just heat from the first cpu. Do the two cpus need to have the same clock rate?

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Old 2021-04-21, 16:20   #29
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Quote:
Originally Posted by henryzz View Post
It should reduce the clock speed if it hits 95C. I don't think you need to worry about it hitting 95C. That said I don't think I would leave it there.
It does feel like the temperature difference is too high. Something is going wrong beyond just heat from the first cpu. Do the two cpus need to have the same clock rate?
I think you're confusing this thread with the drkirby "I put ebay CPUs in a Dell dual-socket server and they don't really work" thread.

That said, I agree with henryzz that the CPU will throttle back around 90C and will not put itself into danger. That's not how we want to do computation, though- pursuing a bigger cooler (all in one water/ radiator maybe? How do you feel about hanging a radiator outside the little case?) should be quite useful.
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Old 2021-04-21, 17:42   #30
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Ok, maybe I'm too worried. The reason the other machine is throttled via PPT to 70 °C is that it sits in my office and even in winter we could go without central heating... So I didn't want to risk my colleague to feel like he's in a sauna once the weather gets warmer. Also the PPT limit did increase LLR times by a meager 1-2 % which I don't mind.


This big difference in temperature comes from the fact that machine #1 is a custom build ATX with a lot of space for fans and a good CPU cooler.


The other one is a Dell with a small tower that is packed with stuff and I guess a mediocre CPU cooler. Installing a larger cooler is not possible due to limited space. I will see how things work out and then decide if I take additional measures for cooling like your advice of an external radiator. Maybe there's space for a second case fan.
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Old 2021-04-21, 19:34   #31
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If the new machine has a factory-installed heatsink, then more airflow is likely to be much more effective at handling peak-power heat than trying to find a new heatsink that will fit.
Even if there is not an empty fan spot, upgrading a factory fan to a high-CFM fan of the same size could get you 5C or more improvement in CPU temp; enough to feel comfortable with temps while also reducing peak-power budget like you have.

The small change in LLR performance under the reduced clock/power budget is likely a sign that the machine is limited by memory bandwidth rather than CPU speed; that's a strong argument for either permanently reducing the power cap, or running LLR on one fewer core (this also might make regular-use programs a bit snappier to respond). I personally run LLR on 3 cores of a 4-core machine when the machine is a compact-prebuilt variety like my employer-issued desktop; I run GMP-ECM on the 4th core, and both heat and memory bandwidth seem happy.
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Old 2021-04-21, 19:44   #32
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VBCurtis, do you mean bandwidth due to L3 cache limit? It's a Ryzen 9 3900x with 16 MB L3 cache per 3 cores. The FFT is at max at 384k, shouldn't that be enough?


That layout should make leaving one core free in total not having much effect, I think since 4 cores share L3 cache, so I'd need to free 3 cores. Or did you mean something else entirely?




For the other machine I'll go with additional and replaced case fans, sounds like a good idea.
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Old 2021-04-21, 21:36   #33
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No, I mean actual bandwidth to RAM. However, if you're running small FFTs like 384k, that is quite unlikely since all the relevant data would fit in L3 cache. Memory requirement is around 6 * FFT size, so a 384k FFT would need roughly 2MB of cache to avoid hitting main memory; I think the Ryzen has far more than this per-core (edit: yes, you said 16MB per tile, in your post- my bad for not paying attention)

On Intel desktop chips with dual-channel memory, the FPU is fast enough to be permanently waiting on main-memory access for all but the smallest FFTs (even 320k sees this happen on 4 cores / 4 instances of LLR). I don't have Ryzen experience, and there aren't many LLR users who study & report on cache use vs main memory bandwidth vs FFT size on modern chips (seems many of us still use Haswell or earlier Intel silicon).

Last fiddled with by VBCurtis on 2021-04-21 at 21:36
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