[SOLVED] At what speed should a CPU start, to be fast for all the tasks that are needed?

[tzuzu100]

At what speed should a CPU start, to be fast for all the tasks that are needed?

 

[USAFRet]

At what speed should a CPU start, to be fast for all the tasks that are needed?

Unsure of your question.

It will "start" at whatever its base clock speed is.
Depending on the particular, it will ramp up to its max Turbo speed, if the workload requires.

 

[tzuzu100]

But will a CPU that starts at 3,5 be not faster than one that starts at 2,7? Even if it will ramp up to turbo boost, the 2,7 cpu
will still not work as fast as the 3,5 one, isnt it so?

 

[USAFRet]

But will a CPU that starts at 3,5 be not faster than one that starts at 2,7? Even if it will ramp up to turbo boost, the 2,7 cpu
will still work not as fast as the 3,5 one, isnt it so?

GHz of the CPU, either base or turbo, is absolutely NOT the only determining factor.

We had a CPU with a base clock of 3.5GHz 15 years ago, the Pentium IV.
A current 10th Gen i7 with a base clock of 2.3GHz is miles faster.

 

[tzuzu100]

What else is an important factor?

 

[USAFRet]

What else is an important factor?

Many things.
IPC (Instructions per cycle), microarchitecture, how the software is written, etc,
https://en.wikipedia.org/wiki/Instructions_per_cycle#Computer_speed

For the IPC - "How many things can it do per clock cycle?"
Instead of applications, lets consider moving people.
I wish to move 65 people down the road 100 miles away. (or running some function/application)

We have a 4 seat Honda Civic going 65mph, and a schoolbus going 55mph.
Which of those will get that 65 people to their destination the fastest?
The bus will, even though the Honda is "faster".
The bus needs to make only one trip, while the Honda has to make several round trips.

 

[geofelt]

Is your question simply academic interest, or is it to determine some action on your part?

Today, modern processors are about comparable in how much work they do per cycle.
In the past, that was not so. Advances in architecture improved the performance per cycle.
With the next 11th gen intel seems likely to advance the efficiency by perhaps 18%.
Good news there.

If a app is designed to only do one thing at a time, then the performance of a single core/thread is all important.
In the example above by USAFRet, the 65mph Honda is going to do the job faster if you only need to transport 1 to 4 riders. It is a relevant example if you are a gamer since few games can make effective use of mote than 4-6 threads.
OTOH, if your work is such that it can be divided into many threads such as editing and rendering apps, then the school bus example is relevant.
We now have from ryzen many cheap thread processors.

There also becomes a limit due to the Amdahl law which shows how the performance of the single master thread
impacts the ability to get the job done.
I think this is an under appreciated aspect of performance.
https://en.wikipedia.org/wiki/File:AmdahlsLaw.svg

Higher clocks are accompanied by higher voltage and temperature.
It make sense to not clock higher unless there is a need.
It is common for a cpu to loaf at 20% speed until there is a need for more.
That is when the faster turbo algorithm kicks in.