Why have CPU manufacturers stopped increasing the clock speeds of their processors? [closed]
I have read that manufacturers stopped concentrating on higher clock speeds and are now working on other things to improve performance.
With
- an old Desktop machine with Intel® Xeon® Processor E3110 with clock speed of 3.0GHz
- and a new server with AMD Opteron(TM) Processor 6272 with clock speed of 2.1GHz
when performed a simple encryption comparison using (single threaded)
openssl aes256c
the desktop performed far better than the server.
So even with latest optimization, why does the processor with the better clock speed perform better?
The reason manufacturers have stopped concentrating on increasing clock speed is because we can no longer cool the processors fast enough for this to be viable. The higher the clock speed, the more heat is generated, and we've now hit a stage where it is no longer efficient to increase processor speed due to the amount of energy that goes into cooling it.
Other answer goes into detail on how higher clock speed doesn't mean better performance in all areas.
There is a lot more to processing speed than the clock rate.
Different CPUs can do different amounts in the same number of clock cycles, due to different variants on pipeline arrangement and having multiple component units (adders and so forth) in each core. While in your test it is not the case, you often find a "slower" chip can do more than a fast ones (measured by clock rate only) due to being able to do more per tick.
The test you performed may be very sensitive to differences in CPU architecture: it could be optimised for a specific architecture, you might find it performs differently not just between Intel chips and AMD ones but between Intel (or AMD) chips of different families. It is likely using a single thread too so is not taking advantage of the CPUs' multiple cores.
There is a move to lower clock rates for power and heat management reasons: ramping up the clock rate does not have a linear effect on power use and heat output.
Because of the above non-linear relationship it is far more efficient for today's requirements to have multiple processing units than it is to push the speed of one unit ever higher. This also allows for clever tricks to conserve power like turning off individual cores when not in use and revving them back up as demand increases again. Of course multiple cores doesn't help a single-threaded algorithm of course, though it would if you ran two or more instances of it at the same time.
Why do you think the manufactures are actually lowering the clock speed by only comparing two processors?
- The 6272 has a Turbo Speed of 3Ghz. The lower base speed is just for lowering average wattage and keeping a acceptable TDP for a workloard when all cores are stressed.
- AMD's next high performance chip for desktop the FX-9590 will hit 5 Ghz.
Also clock-speed isn't the same as performance per clock-cycle. You can have a 3.8 Ghz P4 vs. one 3.2 Ghz core from a i7-3930K, but that doesn't mean the P4 core is faster.
Everything said here about power consumption is also perfectly valid and true for a 16 core design, where you naturally got to be more concerned about TDP issues.
Also your benchmark method just testing openssl is a bit to simple to give real world numbers. Maybe you should try any crypto benchmark suite.
Your test case (aes-256 encryption) is very sensitive to processor-specific optimizations.
There are various CPUs that have special instructions intended to speed up encryption/decryption operations. Not only may these special instructions be only present on your desktop - it might be that the AMD CPU has different special instructions. Also, openssl might support these special instructions only for the Intel CPU. Did you check whether that was the case?
To find out which system is faster, try using a "proper" benchmark suite - or better, just use your typical workload.