Re: How does 2.6 SMP scheduler initially assign a thread to a run queue?

["lk" <linux_kernel@patni.com>]

> 
> In the 2.6 kernel, there is one run queue per CPU, in case of an SMP.
> After a thread is created, how does the scheduler determine which run
> queue it goes to?  

First it forked process (child) gets the same CPU as that of parent.
forking a child gets the same CPU and later part of fork will call 
wake_up_new_task () to fetch the run-queue of the CPU and 
__activate_task () is called to move task into run-queue. 
Later rescheduling of the process may move process to another
run-queues.

>I know that once it goes to a particular run queue,
> the scheduler would try to run that thread on that CPU to take
> advantage of processor affinity; and then there would be the load
> balancing stuff.  But at the very beginning, what algorithm does the
> scheduler use to assign a newly created thread to a particulat CPU?

Child will always goes to the parent's run-queue (CPU) for the first time.

> Would the load balancing algorithm be used? Or gang scheduling?

Yes, load balancing algorithm is used. tasks will be pulled from
very busy processors to lesser busy processors.

> By the way, in an SMT/hyperthreading processor, does the latest kernel
> version assign one run queue per physical CPU, or per virtual 
> processor?
> 

one run-queue per physical CPU

regards
lk

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