New to F@H need startup info

This client will only use a single CPU

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Re: New to F@H need startup info

Postby bruce » Mon Oct 03, 2011 11:47 am

Apparently you're right. Somehow I got the idea it was a laptop. Scratch my comments about laptops and add something like:
If you upgraded it by installing a GPU which generates more heat than the case fans were designed to handle, then you're the one responsible for the overheating and you need to fix the problem by providing better air circulation.
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Re: New to F@H need startup info

Postby Napoleon » Tue Oct 04, 2011 12:09 am

rtbrd wrote:Napoleon, yes when running classic it shows approx. 50% for all logical CPUs, while V7 shows 100% on all logical CPUs. Are you saying that a 5C difference between 50% CPU (8 logical) and 100% (8 logical) is to be expeceted or not unusual?

In this case, yes. Basically, your CPU is capable of scheduling 8 concurrent threads from OS point of view, but it has only 4 FPUs (Floating Point Units). FAH computations are extremely FPU-centric, so 4 active FAH threads (== 4 classic clients/slots) are enough to keep the 4 FPUs (almost) fully occupied. However, 4 active threads / 8 available threads for scheduling is reported only as 4 / 8 * 100% == 50% utilization.

If you execute 8 FAH threads (SMP slot in V7 for example), CPU utilization automatically leaps to 100% (8 / 8 * 100%), but that doesn't change the fact that you have only 4 FPUs. The HyperThreading mechanism will rearrange the execution of the instructions in the 8 threads to make the most of the 4 FPUs. That way HT can increase overall FPU/FAH performance to some extent, but the four FPUs still remain the bottleneck. Relatively small performance gain :arrow: relatively small increase in power consumption and therefore temperature(s).

HT has its pros and cons (mostly pros), but some things about it are counter-intuitive, your case being one of them. Intuitively, 50% to 100% percent leap should be a huge (2x) improvement, but performance of hyperthreaded CPUs isn't a linear thing and it is affected by many factors. In some specific cases it is a great advantage, sometimes it doesn't make much of a difference, and in some rare cases it may even decrease performance slightly.
Win7 64bit, FAH v7, OC'd
2C/4T Atom330 3x667MHz - GT430 2x832.5MHz - ION iGPU 3x466.7MHz
NaCl - Core_15 - display
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Re: New to F@H need startup info

Postby bruce » Tue Oct 04, 2011 8:14 pm

Napoleon wrote:HT has its pros and cons (mostly pros), but some things about it are counter-intuitive, your case being one of them. Intuitively, 50% to 100% percent leap should be a huge (2x) improvement, but performance of hyperthreaded CPUs isn't a linear thing and it is affected by many factors. In some specific cases it is a great advantage, sometimes it doesn't make much of a difference, and in some rare cases it may even decrease performance slightly.


When running code which is not FPU-intensive (i.e.- many things other than FAH) HT can increase performance quite significantly. Unfortunately, the OS does not discriminate between code that saturates the FPU (leaving the ALU mostly idle) and code that saturates the ALU (leaving the FPU mostly idle). All it knows is that 4 or 8 threads are running as fast as they can and it calls one 50% and the other 100%, no matter which internal CPU resource is saturated.
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