Re: [gentoo-user] Re: new machine : CPU : AMD FX-4100 ?

[Mark Knecht]

On Mon, Jul 30, 2012 at 10:14 AM, Michael Mol <mikemol@×××××.com> wrote:
> On Mon, Jul 30, 2012 at 1:04 PM, Mark Knecht <markknecht@×××××.com> wrote:
<SNIP>
>>
>> MB power?
>> Hard drive power?
>> Hard disk power
>> GPU power?
>> DRAM power?
>>
>> The 5 above can easily become the dominant power hogs.
>>
>> I use an Intel i7 980X 6-core hyper-threaded CPU, so that's 12 CPUs in
>> top, which burns _lots_ of power, but I suspect it's not the biggest
>> power consumer when compared to the total of the 6 500GB 7200 RPM hard
>> drives I have in the box.
>
> Spinning disks consume surprisingly little power once they're up to
> speed. My GPU, by comparison, doesn't seem to reduce heat generation
> very much when relatively idle.
>

OK, point taken about the disks at least when talking about a single
disk. I see we measure the same way with a Kill-a-Watt so that's at
least consistent.

And I think we're in more or less violent agreement, but reducing the
CPU power in the end won't save all that much on the electric bill, or
so I think.

I ran around really quickly to find some spec values for the machine
I'm on right now. No idea if the numbers are right. They are just what
I found quickly:

CPU - i7-980x - 130W

vs

Asus Rampage II Extreme - Can't find so far, so let's guess 25W for
the chipset, NICS, audio devices, etc.
WD RAID Edition 500GB - 8W * 6 = 48W
NVidia GTX 465 class card = 80W
24GB DRAM - Total guess, but about 1W/DIMM looks safe, so 6W total

So a __really__ rough guess is my machine should use about (130 + 25 +
48 + 80 + 6) Watts, or 289W assuming I added it up correctly. That's
under full load though. My UPS has a power meter in it. The UPS is
driving this machine, 3 monitors, a small switch, a wireless access
point and maybe one or two other small things I've forgotten or have
plugged in somewhere. When the machine is essentially idle that mater
reads 330W. When I start a VM that uses 6 processor cores and runs for
30 minutes at full tilt the power consumption is 385W. I no longer
remember what I have set up in terms of the CPU clocking stuff. It's
on the machine and let's the box go full tilt, but I'm not sure what
it does when the machine is idle.

Anyway, if you assume that the 55W jump was the difference between the
980x idling, and then using 3 cores full tilt, then 6 cores (12
threads) might be more like a 100W jump which seems about right
according to Intel's spec.

In terms of the electric bill, don't forget the PC power supply is
only 80-90% efficient, so 10-20% is thrown away there also.

Now, assume you get a CPU that draws half the power. This setup would
still likely draw something close to 330W when it's idling, and might
only jump up by 60W when running full tilt. That would save maybe
(330+60)/(330+100) or only about 10% on the whole system power
consumption. For that reason I don't think skimping on the CPU makes
much sense to me. I'll happily turn the box off 2 hours a day vs go
slower all the time, but that's just me.

>>
>> WRT to money spent to run a machine I hope someone stated earlier than
>> this that it's the whole system that matters and not just the CPU.
>
> I didn't state so explicitly, no, but I believe I mentioned the two
> machines had been otherwise comparable in their equipment loadout. If
> I missed that, my bad.

And I don't know that you did as I haven't read the thread, but part
of my argument is that you have to know the WHOLE system and not just
the CPU to decide if changing the CPU costs or saves much power.

Cheers,
Mark