Re: help needed pls. scheduler(kernel 2.6) + hyperthreaded related questions?

[Nick Piggin <nickpiggin@yahoo.com.au>]

Arun Srinivas wrote:
> Pls. help me.  I went through the sched.c for kernel 2.6 and saw that it 
> supports
> hyperthreading.I would be glad if someone could answer this question....(if
> am not wrong a HT processor has 2 architectural states and one execution
> unit...i.e., two pipeline streams)
> 
> 1)when there are 2 processes a parent and child(created by fork()) do they
> get scheduled @ the same time...ie., when the parent process is put into 
> one
> pipeline, do the child also gets scheduled the same time?
> 

No.

> 2) what abt in the case of threads(I read tht as opposed to kernel2.4,where
> threads are treated as processes) ..kernel 2.6 treats threads as threads.
> So, when two paired threads get into execution are they always scheduled at
> the same time?
> 

No.

> Also, it would be helpful if someone could suggest which part of sched.c
> shud i look into to find out how threads are scheduled for a normal
> processor and for a hyperthreaded processor
> 

It is pretty tricky. Basically processes on different CPUs are
scheduled completely independently of one another. The only time
when they may get moved from one CPU to another is with
load_balance, load_balance_newidle, active_load_balance,
try_to_wake_up, sched_exec, wake_up_new_task.