useresp in kernel thread

[Candamir]

I'm now almost done with kernel thread support, the first step in my multitasking system. The only thing I still need to know is what value to give the useresp field (top of tasks stack, I suppose) when creating a new kernel thread. Can I just allocate a block of memory and then set the useresp to the bottom of it? Or would it be the top, as the stack grows downwards?

Candamir

[distantvoices]

top, as stack grows downwards.

[Candamir]

So, this is for kernel threads... And when running a user process, I'll have to look at the executable image to know what's up with the stack, right?

Candamir

BTW: Kernel threads up and running! The only problem is that when a kernel thread is running, the actual kernel (which hasn't finished it's setup yet) isn't allowed to carry on (only interrupts still work... :-\) because the thread consumes all of the CPU time. Is this due to a design flaw or is that like this always? Could this be fixed by first thing, when initializing the task manager, create a task entry for the kernel (which would be set to low priority when the kernel reaches the idle loop)?

[proxy]

you shoudl have a time interrupt with switches between threads, then you should have an extra kernel thread which is always there which doesn't nothing but infinite loop around a hlt.

Now if you use round robin, you should end up with about 50% cpu usage (one thread burning it up, the other just sleeping). Once you end up with priority you'll have 100% usage again...but only when the thread has work to do which is ideal.

Remember the purpose of a scheduler is to give the CPU useful work to do as much as possible. so 100% usage isn't bad, so long as you have stuff that needs to be done.

proxy

[Candamir]

So having a task entry in the linked list for the kernel isn't a bad idea? I would like to be able to do this:

- First part of kernel setup
- Device manager startup, starts a lot of drivers as servers and thus creates many user processes
- Second part of kernel setup
- Idle loop

Candamir

PS: Another aspect of the problem is in another thread by me 'Kernel won't stop running', where I described how I already implemented a part of the solution, but which gives me a page fault when switching to the kernel.

[proxy]

in my OS kenel threads and user threads co-exists seemlessly, the scheduler doesn't even differenciate between the two. Personally, my plan is to use kernel threads for things like bottom half interrupt handlers and the like.

proxy

[Candamir]

@proxy: Do you also have the /kernel itself/ registered as a task with the scheduler that gets it's share of time like a common user process?

Candamir

[Kemp]

surely any kernel code registered with the scheduler *is* a kernel thread, it's just technicalities of what you call it.