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Question about A10-7800 (if possible when in 45W mode)

post #1 of 8
Thread Starter 
I'm thinking to buy a A10-7800 to make a new build but i i want to know something 1st and couldn't find info.

If you own a A10-7800, I like to know when you set it up to 45W cTDP, you still can adjust CPU and iGPU voltages.
In special, i like to know if it allows UNDERVOLT when in 45W cTDP.
Please inform what MoBo are you using. I have a special interest in the FM2A88x-ITX+ but any info about others
will also be appreciated.

TIA,
AJSB
post #2 of 8
i'm avoiding a direct response, c'se I don't know, but allow me to say:
I've got 2 weeks ago, a a8-7600, asus A88XM-A mobo, 16 giga ram Kingston 1800 MHz, Samsung 850 evo 250 gigabytes; I have enabled rapid-mode and a 50-plus giga provisioning on the ssd, I have put the CPU on a 45-watt diet, and my system boots in 3 secs on windows 8.1, and keeps on breaking the 'legal speed limit' , so to speak. the ssd gets 4400 mb/sec sequential read and 2700 mb/sec seq.write. everything is on stock-settings.
post #3 of 8
I have an A10-7850K with the sane motherboard you have and when I set it to different TDP settings I never noticed any changes in it. I guess it's more of a "target" TDP and not the actual TDP.

When I had the target TDO set I was still able to set my voltages/clock speed manually and currently have it running at 3GHz at around 1.000 vcore which puts it in the 45w TDP range. I'll check it more in depth when I get home because I set it a while ago and can't really remember lol.

Sent from my OnePlus One
post #4 of 8
for this mobo, the bios allows smthing like eco-mode; cpuid hwmonitor should reflect the difference in the powers.package wattage, at least for a8-7600; i don't know about the A10-7850K: i suppose you can't cut the tdp in half for the "K" kaveries ...
post #5 of 8
cTDP does not enforce any clock limitations directly but instead it throttles the CPU to keep the power consumption at desired level.

At idle the CPU will work at the same clocks no matter if the cTDP is set to 45 or 95W.
Under load the CPU will adjust it's clocks until the desired power limit is reached.

Obviously the 45W power limit is reached at much lower clocks and voltages than the 95W limit and thats why the clocks will remain significantly lower under the load.

If you want to undervolt the CPU to allow higher clocks at low cTDP limit, then you should use "offset voltage" (negative) function to do so.
Since the CPU will constantly shuffle through many of the available PStates a fixed voltage won't work as no motherboard allows controlling all of the PStates.
post #6 of 8
Quote:
Originally Posted by The Stilt View Post

cTDP does not enforce any clock limitations directly but instead it throttles the CPU to keep the power consumption at desired level.

At idle the CPU will work at the same clocks no matter if the cTDP is set to 45 or 95W.
Under load the CPU will adjust it's clocks until the desired power limit is reached.

Obviously the 45W power limit is reached at much lower clocks and voltages than the 95W limit and thats why the clocks will remain significantly lower under the load.

If you want to undervolt the CPU to allow higher clocks at low cTDP limit, then you should use "offset voltage" (negative) function to do so.
Since the CPU will constantly shuffle through many of the available PStates a fixed voltage won't work as no motherboard allows controlling all of the PStates.

I was wondering if you could elaborate this further. I am thinking of getting an A6-7400K for my parents and running it with passive cooling in 45W mode. My experience is that the AMD chips often can be severly undervolted without problems, which often leads to higher performance when there is a power limit (Undervolt R9 Nano = Win).

I have read several posts from you about Steamroller and the broken power management. wink.gif Could I still expect to unlock performance from undervolting this chip, or does the chip not recognize the higher TDP-headroom?
post #7 of 8
Athlon X4 845 has 5600 passmark vs. 2800 for a6-7400k , at the same tdp . x4 845 has 4 carrizo cores, which is the best thing until zen arrives.you could couple it with a r7 240.
Edited by costeakai - 7/26/16 at 10:28pm
post #8 of 8
Quote:
Originally Posted by Flash831 View Post

I was wondering if you could elaborate this further. I am thinking of getting an A6-7400K for my parents and running it with passive cooling in 45W mode. My experience is that the AMD chips often can be severly undervolted without problems, which often leads to higher performance when there is a power limit (Undervolt R9 Nano = Win).

I have read several posts from you about Steamroller and the broken power management. wink.gif Could I still expect to unlock performance from undervolting this chip, or does the chip not recognize the higher TDP-headroom?

Every AMD APU/CPU prior Excavator uses hardcoded power management. That means lowering the actual power consumption by undervolting or improving the cooling yields no additional performance improvements, unless the chip was thermally limited to begin with (overheating and throttling because of that). So basically undervolting these will just reduce the power consumption, but yields no additional performance benefits.
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