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albright
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PostPosted: Thu Jul 17, 2014 1:29 pm    Post subject: undervolt i5-4300u [SHELVED] Reply with quote

Hi all - I have a thinkpad T440S with intel i5-4300U processor

there is a windows app from intel that permits undervolting (which
lowers temps and improves battery life)

I wonder if there is anything for linux (phc-intel does not seem to
work though that is not entirely clear to me; also maybe issues
with p-state governor ...?)
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Last edited by albright on Tue Jul 22, 2014 2:52 am; edited 1 time in total
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pa1983
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PostPosted: Mon Jul 21, 2014 5:14 am    Post subject: Reply with quote

Modern processors adjust voltage according to frequency so I cant say I see the point realy. My experience is that voltage is so low at idle that lowering it causes instability and boot failures.
You can google your CPU and find the voltage range it operates with in on intels home page. Even my i7 3930K stock runs as low as 0.6 according to spec.

Best thing to do is to make sure intel C-STATES work properly, enabled in bios and the verify with i7z that the CPU goes in to C6 or deeper state at idle. That cuts power completely 99% of the time so cant save much more power then that.
I use that on my i7 even when its overclocked, gives low idle power use but i get plenty of power when needed at the cost of high power draw from overclocking.

My view is that people still thinks of modern processors as the good old classic processors with fixed clock and voltage. Thats not the case and has not been for years. So usually adjusting voltage manually to a fixed on and lowering clocks by removing turbo functions will probably give worse performance/watt.
A big part of the power consumption on a processor is leaking current. 40% or so. So its often better to execute code fast at high power use but at a very short time since leaking current happens as soon as the processor is powered on so the faster it works the less power is actually wasted and more is used for computation.
So a faster CPU will go execute faster (C0 state) and then go in to deep sleep faster (C6 state) wasting less power.

Modern processors are very optimized for performance per watt at any type of load and they them self monitor all parameters to determent the optimal settings for voltage, frequency etc.

Best thing to do In my book is to just make sure this works properly. i7z is a good tool to check that a CPU can go in to deep C states and can adjust clocks properly according to loads.
BIOS and kernel effects how this works so never a bad idea to check that it works properly.
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haarp
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PostPosted: Mon Jul 21, 2014 1:46 pm    Post subject: Reply with quote

Forget PHC, first-generation Core2 were the last CPUs that worked with it. Forget p-states, they are not very relevant in modern turbo-capable CPUs anymore.

If Intel released a fancy tool that allows undervolting, it's probably writing some magical MSR. Your best bet is to trace what it's writing and replicate that under Linux.
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albright
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PostPosted: Tue Jul 22, 2014 2:52 am    Post subject: Reply with quote

I tried the windows intel utility; unfortunately my chip is
not of the highest quality and could only undervolt
stably about 80mv

seemed to drop stress temp a tiny bit so this is not
worth pursuing I think
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