How do OS's handle hyperthreading?

[d4mo]

Like on an i7 for example is the OS smart enough to assign one thread per physical core before assign 2 to one?

For Example

Core 1
Logical core 1 - Thread
Logical core 2 - Nothing

Core 2
Logical core 1 - Thread
Logical core 2 - Nothing

Core 3
Logical core 1 - Thread
Logical core 2 - Nothing

Core 4
Logical core 1 - Thread
Logical core 2 - Nothing

 

[Phynaz]

Windows does exactly that.

 

[Cogman]

Yes. Scheduling is pretty smart and pretty complex on the OS level. OSes do a lot of work to try to keep your CPU as busy as possible. The OS scheduler needs to take into account things like core affinity to make sure that you aren't getting a bunch of cache misses because your thread is leaping across cores (memory -> CPU is expensive).

 

[BTRY B 529th FA BN]

Can the OS Scheduler be manipulated via registry?

 

[videogames101]

Can the OS Scheduler be manipulated via registry?

You can go look around and edit the linux scheduler if you want 🙂

http://lxr.free-electrons.com/source/kernel/sched/fair.c

 

[tweakboy]

Depends,, In due time things will go full x64 but thats a long time from now.

 

[Cogman]

Generally, no.

Scheduling is one of those core things that OSes do. They try to provide flexible schedulers that are very general purpose. Some OSes will allow you to change the scheduler that is being used to help optimize it for the system task (different scheduler for a database for example). But those are generally OSes geared towards servers and not end users.

It is best not to futz around with the scheduler. The guys that write these things put blood, sweat, and tears in them to make them work as fast and as efficiently as possible. Almost anything you would do will negatively impact your system's performance.

One way you can influence the scheduler is by bumping the priority of whatever it is you care about. In linux this is the "nice" value and in windows you can change it from the task manager. Be warned, though, if you do something like set a bunch of tasks to realtime which are CPU intensive, you can pretty much take down your OS. The scheduler will starve the OS in favor of running your app.

 

[Borealis7]

in a pure CompSci theoretical sense, the OS shouldn't know the difference between logical and virtual cores, and it shouldn't matter to the OS. in reality - it knows.

 

[Magic Carpet]

Like on an i7 for example is the OS smart enough to assign one thread per physical core before assign 2 to one?

Smart enough, unless you are using Windows 95 or something 😎

 

[Heatshiver]

If that interests you, you should also look into core parking. Some related info there which can be interesting to learn and try.