Quick HyperThreading question

[Darkfalz]

If something is only using one thread, a very CPU intensive thing like
WinRAR, is it only using 1.5 GHz of my 3 GHz CPU?

Because when I look in task manager it shows 50% CPU in use and 50% idle!

 

[Jens Baumann]

If something is only using one thread, a very CPU intensive thing like
WinRAR, is it only using 1.5 GHz of my 3 GHz CPU?

Because when I look in task manager it shows 50% CPU in use and 50% idle!

No, it DOES use the full 3GHz power, just as if you had a non-HT-capable
3GHz CPU in your machine. Hyperthreading just gives an added "boost".
compared to a non-HT CPU. Task Manager is confused because one logical
processor is showing up as idle, so it thinks "one CPU full power, one
CPU nothing to do, that's 50% of what is possible" - but it fails to
consider that the 2nd logical CPU is not a real one (e.g. no separate
cache) and that the added boost for multi-processor aware software is
only about 10-20%, depending on the exact kind of software.

In other words: everything OK, no reason to worry.

 

[DaveW]

It doesn't work like that. One thread will use up to 100%.

 

[Robert Hancock]

Well, yes and no, in a way. Anything that uses only a single thread will not
take full advantage of a HT-capable CPU. However, the two execution threads
share resources on the CPU die, so the performance will not double when
using both threads.