Why do the fans start when one core is maxed out

[xwb]

I'm running VMs on a core i7. I had one core assigned to a VM. During a build, within the VM, CPU usage is 100%, 12.5% on the host and the fans go crazy.

I then assigned 2 cores to the VM. 25% on the host and the fans are still going crazy.

I then assigned 4 cores to the VM. 50% on the host and the fans are normal.

Don't understand this: why is it when 4 cores are used by the VM, the PC doesn't need as much cooling as when 1 core is used? The same happened on a Xeon.

 

[stduc]

I would assume that it is to prevent a core overheating. Presumably there is a thermometer per core. As you don't have a fan per core if one core gets hot it has to go to max cooling for safety's sake. What I don't understand is why you say 4 cores used 50% of the CPU. If 2 cores used 25% (each at 50%?) then I would expect 4 cores to use 12.5% each at 25%.

 

[paparazi]

Unrelate I guess but:
Thats why I don't like stock coolers, where then fan sounds excessive and load at 100%.
I use a large heatpipe cooler with 120mm fan so in the unlikely even (given it's improved cooling over stock) that the fan spins at full speed, it is still barely audible.
I use a Fenrir Titan but there are many others out there at a reasonable cost which will lower CPU temps but at the same time dramatically reducing noise.

http://www.guru3d.com/article/titan-ttcnk85tz-fenrir-cpu-cooler-review/

Martin

On wings like angels whispers sweet
my heart it feels a broken beat
Touched soul and hurt lay wounded deep
Brown eyes are lost afar and sleep

 

[xwb]

It has 8 cores so 1 core=12.5%, 2=25%, 4=50%, 8=100%. I've allocated 4 cores to the VM so when the VM is maxed out the host is running at 50%.

With a laptop, there isn't a lot of chance changing the fan. Dells have made stuff so difficult to modify it is even a pain adding memory or upgrading the disk. This used to be really easy on the older machines.

 

[paparazi]

My appologies, with 8 cores i presumed it would be a work station.
Thats one powerful laptop you have there.....

Martin

On wings like angels whispers sweet
my heart it feels a broken beat
Touched soul and hurt lay wounded deep
Brown eyes are lost afar and sleep

 

[stduc]

Ah - I see what you mean now! That is a bit of a puzzle. Do you have any CPU temp monitoring software? Have you tried running resource monitor. On an I7 you actually have 4 cores each multi threaded so you get 8 threads not 8 CPUs. I did a bit of testing for you on an I7 running Win 7 Ultimate using Excel 2007 and running a large macro. This is what I found.

Fan	CPU	Cores		Cores
Speed	Temp	Requested	Used
RPM	deg C			%

527	34	N/A		N/A	Idle state
1406	55	1		4	1 at 75% 1 at 50% 2 at 10%
1500	55	2		4	2 at 75% 1 at 50% 1 at 10%
1500	55	3		4	2 at 75% 1 at 50% 1 at 10% 
1500	55	4		5	3 at 75% 1 at 50% 1 at 10%
1500	55	5		6	4 at 75% 1 at 50% 1 at 10%
1500	55	6		7	5 at 90% 1 at 75% 1 at 50%
1550	63	8		8	8 at 100%

That table is a bit of an estimate as up to 4 cores requested the actual 'core' used kept changing! Also the graphs were up and down a bit.

I can only conclude that Excel & or Windows is not that good at core limitation and a lot of stuff is going on. I did it with Excel because you can change how many cores quickly unlike with a VM where you have to reboot the VM each time.

I hope, but doubt, this helps you much. Let's hope a real expert notices this thread and replies.

 

[xwb]

Had a grope around. My machine doesn't have any temperature monitoring or fan speed S/W attached to the resource monitor. I'll have a look on the net; maybe Dell have some tools for this.

 

[rclarke250]

speedfan can be used to monitor the fans,

http://www.almico.com/speedfan.php

 

[xwb]

Thanks I'll give it a spin tonight

 

[gbaughma]

Holy Schneikies! I see why they call that cooler the "Titan".



Just my 2¢

"What the captain doesn't realize is that we've secretly replaced his Dilithium Crystals with new Folger's Crystals."

--Greg

http://parallel.tzo.com