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Core Affinity on AMD FX Processors

Mon Nov 12, 2012 11:34 pm

My friend recently bought a Trinity Laptop (A10-4600M, Windows 8) and he wanted me to set it up and test it. First thing i did was run Prime95 and Coretemp to make sure it wouldn't overheat. During my first run of Prime95, i set it to 4 cores. When i did that, the multiplier on all 4 cores constantly jumped up and down in Coretemp (From 8.5 to 13.5, i think). I re-ran the test with only 2 cores and the multiplier for all 4 cores was 13.5 throughout the entire test.

I didn't think that meant anything until he downloaded Borderlands 2. They (My friend and my brother) had set the core affinity to (all cores) for some unknown reason, and asked me why the game was running choppy. I explained the whole module thing and set the Core Affinity to cores 0 and 2, and the game began running properly.

There are a few things im wondering regarding this.
1. Did the multiplier jumping have to to with a Turbo boost or Cooling feature in the laptop?
2. On a Desktop FX CPU, Do you think setting the Core Affinity to even cores (0,2,4, and 6) on games increase/decrease performance? (I remember reading that Hyper threading on i7 processors lowered performance in games when compared to I5 processors by 5-10% in one of the initial reviews of the Sandy Bridge ones, and that disabling it was suggested).
3. If someone with an FX Processor can test out question 2.

Decided to also google this before posting, and this is what i found. ... heduling/2
Couldn't find any benchmarks on games regarding core affinity, but it does state there that "In every case but one, distributing the threads one per module, and thus avoiding sharing, produces roughly 10-20% higher performance than packing the threads together on two modules". It also states that the scenario may or may not be the same in games (But if i knew that for certain, i wouldn't even be posting this thread)
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Re: Core Affinity on AMD FX Processors

Tue Nov 13, 2012 12:48 pm

Pretty sure the multiplier weirdness is related to the fact that all cores can't run at turbo speed simultaneously. It is probably dropping cores in/out of turbo mode based on how many cores have running threads on them.

Not sure about the thread affinity issue. I suspect it will help some, but that the effect will be small since (unlike hyperthreading) the entire core isn't being shared, just parts of it.
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Re: Core Affinity on AMD FX Processors

Tue Nov 13, 2012 1:01 pm

If you tinker, try to lower the voltage... Also check your CPU core temperature.
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Re: Core Affinity on AMD FX Processors

Tue Nov 13, 2012 3:15 pm

I don't know how much use what I am about to say is, but I have given up trying to get my 8120 to hold steady clock speeds or use TurboCore properly. I'm certain it lies with MSI's BIOS doing something a little weird, but I can't be sure and don't have the time to do some detiled troubleshooting.

I try to run my FX at an OC of 4.8 Ghz (200 * 24), with CnQ turned on and Turbo Core. When I run this set-up, from time to time when I say stress the CPU's 8 threads (I had choose 8 ) in Prime95, it either:
- Does not clock up the CPU from idle state. It stays at 1400Mhz per core as per idle conditions or will fluctuate between idle and OC (or stock speeds as in your case). Or...
- Clocks up to it's rated Turbo Core speed (4 Ghz), but only 4 threads show activity (I chose 8 ).

If I run the OC as before, but turn off Turbo Core at BIOS level, the 2nd problem above never happens. All 8 "cores" ramp up to 4.8 Ghz in that scenario. Sometimes idle state is still invoked for whatever reason with Turbo Core turned off, and it's seemingly at random. Only way I stopped that happening was to turn off CnQ, but then it leaves the FX at 4.8 Ghz all the time (Eeeeek, the power consumption). Stock speeds don't make any difference neither, one or both of the above still happens.

It doesn't get hot enough to be clocking back. Under max CPU load with the CF Radeon's going into meltdown heat wise, the CPU hovers at about 50-60C on the 4.8 Ghz OC. Idles in the high 20's to low 30's otherwise.

IMO, Turbo Core seems broken, as it shouldnt ramp up to 4 Ghz anyway when it's got 4 thread workload acording to AMD, and it looks like Core Parking or thread scheduling isn't working properly. It's the only reason I can think of causing the issue of an 8 thread workload only being split across the FIRST 4 threads in Task Manager. Half the CPU appears to be asleep, and performance suffers. Scheduling the workload properly over every other "core" first makes a small improvement according to the benchmarks, but W7 doesnt do this but apparently W8 does with a dozer CPU...

Either way, mine does the same strange behaviour as yours, and welcome to TR. :-)
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