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.

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