AMD Athlon64 4000+ Underclocking

Bios_Hakr writes "PC Stats is running an article on their experiences underclocking an AMD 4000+ processor. Their goal was to try and reduce the voltage requirements and lower the heat output. They benchmark using 3dMark01, 3dMark05, as well as SuperPi. From the article: 'This got us thinking though; what about under-clocking? Most modern processors and motherboards can just as easily run under a rated speed as it can run over... but is there a point to this? Well possibly.'"

Re:Don't keep us in suspense

[lukewarmfusion]

The point is...

Suspense = more clickthroughs = more ad views = more revenue.

Underclocking makes sense to me

[Dolphinzilla]

If you are designing a system for high reliability, under temperature extremes and such (military environments for example) underclocking is the way to go - you can minimize power and heat loads as well as potentially avoid timing instabilites that occur when you push a processor to the performance margins.

Er, did they hear about Cool'n'Quiet?

[marat]

I thought what they are testing is the whole point of AMD Cool'n'Quiet technology, but they don't even mention it in the article! Nice try reinventing the bicycle. I'm already underclocking my Athlon 64 right now, thank you.

What's the point with passive cooling...

[TERdON]

... if there are annoying fans on the motherboard as well as on the GPU?

You would think the whole point gets moot - the system certainly won't be quiet. (I believe there is an actual need for quiet systems eg in recording studios etc - which make the article interesting, but not great).

Low-power computer with commodity parts

[tepples]

If you want low power you can buy systems specifically designed to perform well on low power supply.

The article is about researching how to build such systems out of cheap commodity parts, unlike the proprietary, often Windows-only parts found in laptop computers.

Not useful information?

[erroneus]

I think it is somewhat useful information. While most people are thinking about how much faster you can process, many of us are looking to reduce the noise of fans blowing. I recall when 800MHz was a fantastic speed... hell, for that matter, 300MHz was pretty nice too depending on how far back you go.

And are we really using all of those cycles? Not really. Right now, a system's performance (IMHO) is largely the responsibility of the quality of RAM, Video and system board stuff. After all, what "feels" fast must be fast. If I've got a slow hard drive, then it's a slow system and if I can accellerate the video, then it's a slow system. What good is 4GHz if you've got a slow everything else... and by the same token, if you've got a fast everything else, a 2GHz processor is probably plenty.

Their Maths is a little suspect in places

[kabbor]

They listed the drop in temperature from 33.5 to 26.9 as a 20% drop. However, they didn't mention the ambient temperature. If you take 20 degrees, then this drop is more like 50%. That would also mean that it was consuming well under half the power. (I'm assuming watts->degrees is exponential.)

As a secondary matter, the person who got me interested in BSD, as a rule, made his servers with whatever was the cheapest AMD-K6, underclocked to 350MHZ. Bulletproof boxes with long lifetimes. I'm sure there are still some churning out the bits around this town.

There is a point...

[chihowa]

On all of my personal must-stay-up servers, I get a processor that is too beefy for the task it's to do, then clock it down. It's usually rock solid and runs very cool. In some cases I've been able to get by using only passive cooling and still keeping the processor very cool, making the system solid, cool, and nearly silent.

Re:Don't keep us in suspense

[PsychicX]

I don't get it. If you wanted a low power system, why would you buy the top chip and underclock it?

The Athlon64 4000+ is a Hammer chip, iirc. It's manufactured on a 0.13nm process, and is a slightly older core. Instead of using that chip, why not use the Athlon 3800+? The Winchester and Venice cores are both 0.09nm chips, and run much, much cooler and dissipate much less heat than the Hammer cores. And you can use AMD's Cool n Quiet (aka PowerNow) technology to back off the processor speed to half speed automatically, when the processor isn't seeing heavy use. Coupled with a utility like RMClock [rightmark.org] on windows or a custom written utility on Linux (if your 2.6 kernel has the necessary options enabled, you simply have to write to some files in /sys), you can undervolt the chip even more than AMD's driver allows. My Athlon64 3200+ spends most of its time at 1 volt, 1 GHz, and it runs at ambient temperature. That's right, the heat generated is so little that on a stock cooler, the processor does not raise its own temperature significantly. And if a 3800+ with CnQ is too powerful, you can back down to the 3500, 3200, or 3000 models, depending on your exact needs.

Problem solved, and without several pages of blathering about underclocking.

Faulty Analysis?

[Brian Blessed]

The temperature measurements in the article don't seem to be relative, and yet they say things like this:

for a 66% drop in speed there was a 20% drop in temperature.

In this context, talking about a 20% drop in temperature in degrees celsius makes no sense for comparison purposes. They go on to state that "a 43% drop in voltage producing a 20% drop in heat seems more reasonable", but this is assuming that the temperature drop corresponds to a equal reduction in heat output.

- Brian.

Mistake

[Richard_J_N]

They have measured the (absolute) celcius temperature of a well-cooled system, without quoting the ambient temperature. Then, concluding that the temperature hasn't droppped much, they assume the power hasn't dropped much.

The correct measurement is the *difference* in temperature between the CPU and the ambient air. Power dissipation is linearly proportional to this.

Re:Don't keep us in suspense

[pla]

a very fast, very hot modern processor (in this case an AMD Athlon 64 4000+)

Very hot? If you haven't already bought one, just make sure to get one with a Winchester or Venus core.

Using C&Q, mine (only a 3000, but "close enough" to make my point) could probably get away with purely passive cooling. Using a meter at the plug, it draws a whopping 54 watts average, with 48W idle (C&Q engaged) and 65W max.

Thanks to modern CPU power saving technologies as implemented in all newer Athlons and Opterons, or Pentium M, you really don't need to sacrifice peak performance for the sake of power and heat. They deal with usually sitting there idle fairly well, by throttling back, without needing to resort to such (relatively) drastic measures as "suspend" and "hibernate".


I do, however, see one possible use for underclocking... When you keep your CPU always pegged at 100% (running Seti @home or the like, for example). Then, underclocking would allow you to trade a little bit of performance for a lot of power and heat reduction.

Re:Umm....

[ccccc]

Well, the whole point for Cool & Quiet is that this can be done dynamically during run-time. It's quick and painless for your fast processor to slow down when you don't need the horsepower. The slower processor can't suddenly become faster if you need it.

Idle?

[CustomDesigned]

My system is never idle. It runs seti@home and/or folding@home 24/7 in the background. So I don't think the power saving features will work for me if they depend on the processor being idle. I bought a Dell 500SC for home. It has been rock solid, but the fan is very noisy, and the DMA on the secondary IDE is busted (chipset bug). When I upgrade, I don't care about bleeding edge performance, I want it to be quiet. Wouldn't you know, after I bought the 500SC, Dell came out with the 400SC, which I've installed at several customers. That thing is quiet as a mouse. Sigh. I thought about switching and telling them, "See, 500 is better 400!"

Re:Don't keep us in suspense

[shawb]

I think the power supply requirements are more based on a gamer rig than your everyday Joe workstation. Incredible video cards, multiple hard drives (possibly in RAID configuration striped for speed,) overclocking, cooling systems, and then bling (flourescent lights, etc) all suck down power. I doubt that a power supply will always draw it's peak power, so having a litttle headway is worth it to keep the system a little stable.

Makes complete sense in large data centers

[micron]

I am extremely glad to see "underclocking" gaining in popularity.

I design systems that run applications across hundreds or thousands of servers. Many of my applications are bound by items such as connections, long before processor becomes a bottleneck.

As a case example, I will have an application that utilizes 55% of the proc across two processors. I use two processors to keep response time down (multi threads). Intel gives me a new processor. I get to spend more money to power the new processor, but now I get the amazing advantage of the new, faster, more power hungry machine now being 30% utilized.

More money down the drain, but I am not getting much for it. The worst abuse of this is static content web servers. I run into connection issues and network latency issues long before I run out of processor.

With the new HE processors from AMD, I can turn down the processor clock and cut my power consumption by as much as 50% across the board. This translates into real savings on power and cooling infrastructure.

Re:Underclocking makes sense to me

[ignorant_coward]

For high reliability, I'd just buy a pre-engineered system from IBM or Sun rather than put on my engineering hat and pretend I know what I am doing.

For hobbyists, all this is good and fun, but I'd hate for my anectdotal experience of one machine running underclocked well to be the underpinnings of a business webserver.

Re:There is a point...

[Anonymous Coward]

not trying to be a jackass.. but why do you have "must-stay-up" servers that have to be quiet?

I don't know about quiet, but if his servers don't need fans, that's one less thing to fail.

Quiet is just a bonus.