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Shared cache? Power down individual cores?

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October 9, 2007 5:21:03 AM

Hello. I had some technical questions about the Intel quad core chips that I was hoping that someone here might know about...

On the Intel Quad Core chips, and each core access the >entire< cache? Or is is only shared with one other proc? I notice that the cache size is listed as 2x4MB, not 8MB, which prompted this question.

I've also heard that individual cores can be powered down via the /proc interface in Linux ; is this true for Core Quads? And if so, does it actually lower the power consumption an appreciable amount?


I'd really like to build a new system when the 45nm processors come out, which is why I am looking into this. Unfortunately, none of the mini/booksized PC's seem to support FSB1333 yet, so I'd have to build my own case around a microATX mobo (ugh, a lot of work).

Thanks,
Andrew
October 9, 2007 7:08:51 AM

Remember there 2 Dual core stuck together(In loose terms). My basic understanding that each set of 2 cores share 1 cache and that doesn't change. eg. CORE 1 & 2 share cache one, CORE 2 & 3 share cache two. :) 

Could be wrong, but thats my understanding. Not sure about your other questions. :p 
a c 139 à CPUs
October 9, 2007 7:20:56 AM

A core 2 quad is just 2 core 2 duos stuck together. As such 2 cores share a cache(4megs) and the other 2 share another(4megs)

I do not think you can power down cores.

Speed Step(clocks down and reduces voltage) and CE1(think thats what its is called....reduces voltage) will both lower power usage..... In my case this saves about 50-60 watts at idle

But once any core is loaded they all clock back up. There is still a power savings at this time...

New cpus will be able to turn off cores(I think AMD Phenom is supposed to do this) and save allot of power(well more at lease). There are also some plans for cores running independent speeds to save power as well....

So in short the core2 quads are not that bad on power anyway....but new intel and amd chips will be better for power and heat......

EDIT

martyjs beat me to it
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a c 102 à CPUs
October 9, 2007 3:35:59 PM

Quote:
A core 2 quad is just 2 core 2 duos stuck together. As such 2 cores share a cache(4megs) and the other 2 share another(4megs)

I do not think you can power down cores.


Nope, not on desktop chips. Laptop chips have much lower sleep states (C4) that can pretty much do this, though.

Quote:
Speed Step(clocks down and reduces voltage) and CE1(think thats what its is called....reduces voltage) will both lower power usage..... In my case this saves about 50-60 watts at idle


You shouldn't see such a drastic difference between idle wattage draws at full speed and full Vcore vs. idle speed and idle Vcore, especially not in an Intel CPU. At best, your Core 2 Quad goes from 2.93 GHz down to 1.67 GHz at idle and drops about 0.15 volts Vcore or so. I'd imagine a wattage savings of something nearer 20 watts than 50-60 watts. Now if you are talking about running the CPU at full-load under idle settings vs. full-speed settings (via setting power properties), then you should see a big difference like that.

Quote:
But once any core is loaded they all clock back up. There is still a power savings at this time...


This is true with all K8 CPUs and desktop Core 2 Duos. However, the mobile Core 2 Duos have separate C-states for each core. It isn't apparent to me if the cores clock separately or not. Cpufreq says they do, but I can't find it anywhere in the Intel literature. So even if the core clocks and voltages are the same for both cores, the idle core will have parts shut off because of the C-states and save power. The AMD 10h family processors *do* have the ability to separately clock cores, even though the Vcore is the same for all cores. I assume they will have C-states that vary per core as well.

Quote:
New cpus will be able to turn off cores(I think AMD Phenom is supposed to do this) and save allot of power(well more at lease). There are also some plans for cores running independent speeds to save power as well....


The higher C-states can shut off large parts of idle cores to save power. The C6 state in the Penryn Core 2 Duo mobile chips pretty much does shut off the core.

Quote:
So in short the core2 quads are not that bad on power anyway....but new intel and amd chips will be better for power and heat.....


The current Core 2 Quads are pretty bad on power, to tell the truth. The slowest one is the Q6600, with a 105-watt TDP. That is pretty warm. The faster ones go up to 130 watts, which is as hot as the hottest Pentium Ds ever were. 65 nm is great for dual-core CPUs, with 3.00 GHz units from Intel using 65 watts and AMD's 6000+ using 89 watts. But it's a little premature for high-clocking quads. Intel has some quads with reasonable TDPs, such as the 50-watt Xeon 5300LVs and 80-watt Xeon 5300 series from 1.60-2.33 GHz. AMD also has some very reasonable quads, with TDPs of 68 watts up to 1.90 GHz and 95-watt TDPs to 2.00 GHz. Sure, they can push TDPs to 125 to 130-watt levels to get a few hundred more MHz, but I think that it would be smarter to wait for smaller process nodes or greater process refinement to start pushing speeds higher rather than raising the TDP ceiling.
October 9, 2007 4:15:08 PM

Although you can power down individual cores, the feature is only available in Core 2 duo Merom (laptop), as MU_engineer said. Other than that, currently Core 2 Quad does not support split power saving (different from split power plane).

I don't know if its a good thing to have split power plane on quad core though. K10 implemented the feature, and they're suffering from massive latency issue.
a c 102 à CPUs
October 9, 2007 4:16:53 PM

zenmaster said:
Actually, the Q6600 and Q6700 are only 95w.
http://processorfinder.intel.com/details.aspx?sSpec=SLA...
http://processorfinder.intel.com/details.aspx?sSpec=SLA...

The x2 6000+ is actually 125w
http://www.bit-tech.net/
hardware/2007/02/22/amd_athlon_64_x2_6000/1


That's right with the G0 revision of the Q6600 and Q6700- they are 95 watts. The B3 stepping of the Q6600 (SL9UM) was 105 watts and the B3 stepping of the Q6700 (QX6700, SL9UL) was 130 watts. The 89-watt X2 6000+ was supposed to have been released already, but apparently it will in Q4. The Opteron 2222 (NOT the 2222SE) has already been released and has similar ratings as the new lower-TDP 6000+.
a c 139 à CPUs
October 10, 2007 12:29:10 AM

Here's my numbers....
Note that in my case the numbers come from my ups and it runs 2 computer, 1 screen, 1 router, 1 switch, 1 cable modem and my cordless phone base. There is also a external drive(turned off)...would now want a power out to mess with my backups...All other items on the ups use about 210-230 watts on average

Load f@h SMP - 9 x 333 - 3.0


Idle - 6 x 333 - 2.0


Looks like i do get my 50-60 and then some....

And as said above... G0's are 95....thats not bad when i compare it to my A64 3200+ at 89. Its is also not bad since its less than ~30 watts more then my E6600. 30 watts for 2x the cpu power. Yeah its all good to me.
a c 102 à CPUs
October 10, 2007 3:14:04 AM

nukemaster said:
Here's my numbers....
Note that in my case the numbers come from my ups and it runs 2 computer, 1 screen, 1 router, 1 switch, 1 cable modem and my cordless phone base. There is also a external drive(turned off)...would now want a power out to mess with my backups...All other items on the ups use about 210-230 watts on average

Load f@h SMP - 9 x 333 - 3.0
http://img513.imageshack.us/img513/9691/loadah5.gif

Idle - 6 x 333 - 2.0
http://img253.imageshack.us/img253/6172/idlepz1.gif

Looks like i do get my 50-60 and then some....

And as said above... G0's are 95....thats not bad when i compare it to my A64 3200+ at 89. Its is also not bad since its less than ~30 watts more then my E6600. 30 watts for 2x the cpu power. Yeah its all good to me.


Your images say it all- you are comparing idle clocks and no load to full load and full clocks. You'd certainly expect to see 50-60+ watts, and since you're figuring the draw at the UPS, your PSU and VRMs too. That's what I said. You said in a previous post that 50-60 watts was saved when your chip would use EIST to throttle from 9x333 to 6x333. That's not true- almost all of that power was saved because you turned F@H off and reduced the load.

Here's what you should do to test how much power EIST saves you. Have the computer run off the UPS so you get the wattage reading. Do this first at EIST idle as you did before and got 421 watts. Now go to your power properties and select "Home/Office Desk" which disables EIST. Now the CPU will run at full speed and then check the UPS draw. My guess is 10-20 watts at most more power is drawn.
a c 139 à CPUs
October 10, 2007 3:51:25 AM

i only said load to idle in the first place

"In my case this saves about 50-60 watts at idle"

This is not worth fighting over....all i said was that from CE1 and Speed Step....i save power at idle(as opposed to being loaded)....

I will turn off CE1(with this on even at full clock speed the cpu voltage is reduced anyway...) and Speed step to get better measurements(as soon as i get a chance...).

I still stand by my statement that Quad cores are not as power hungry as people think when compared to duals(especially last generation of them). And that Speed Step and CE1 save me power....even if its only a little(i will test it)....

You use linux?
a c 102 à CPUs
October 10, 2007 4:00:39 AM

Quote:
i only said load to idle in the first place


Sorry, I must have mis-interpreted what you meant.

Quote:
I will turn off CE1(with this on even at full clock speed the cpu voltage is reduced anyway...) and Speed step to get better measurements(as soon as i get a chance...).

I still stand by my statement that Quad cores are not as power hungry as people think when compared to duals(especially last generation of them). And that Speed Step and CE1 save me power....even if its only a little(i will test it)....

You use linux?


Yes, I do use Linux. My desktop uses Gentoo 2007.0 AMD64 and my laptop uses openSUSE 10.3 x86_64.
a c 139 à CPUs
October 10, 2007 4:09:58 AM

hmmmmm.....whats a good linux media center(DVD, XviD, DivX, Mpeg, ect)...

I have a project for a small media player(TV use only, remote control input)...and windows adds cost for nothing...
a c 102 à CPUs
October 10, 2007 4:13:32 AM

nukemaster said:
hmmmmm.....whats a good linux media center(DVD, XviD, DivX, Mpeg, ect)...

I have a project for a small media player(TV use only, remote control input)...and windows adds cost for nothing...


MythTV http://www.mythtv.org/ is what I use. It works quite well for that purpose with my Hauppauge PVR-150 card.
a c 139 à CPUs
October 10, 2007 4:44:58 AM

I will give it a try...

[/Hijack thread] - Better stop now

EDIT

11.8 megs....WOW impressive compression
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