[uml-devel] Regarding Process creation in UML tracing thread mode

[uml-devel] Regarding Process creation in UML tracing thread mode

[Krishnappa Abhijith-A21204]

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Hi,
             Regarding fork() implementation UML in tracing thread (tt)
mode
Whenever we call fork in UML the following happens:
 
2 process gets created 
1 on UML say U_1 and 1 on HOST say H_1
 
Process in host gets created by tracing thread but how does a process in
UML gets created ?
 
Also whenever a UML process makes a system call UML uses the
corresponding Host process for execution of system call is that true ?
 
Also, How does UML process communicates to irts corresponding host
process
 
 
 
Thanks a lot for all the help.
 
Regards,
Abhi
 

 

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Re: [uml-devel] Regarding Process creation in UML tracing thread mode

[Jeff Dike]

On Wed, Mar 21, 2007 at 07:51:44PM +0800, Krishnappa Abhijith-A21204 wrote:
>              Regarding fork() implementation UML in tracing thread (tt)
> mode
> Whenever we call fork in UML the following happens:
>  
> 2 process gets created 
> 1 on UML say U_1 and 1 on HOST say H_1

No, one process gets created, in which both the process and the kernel run.

				Jeff

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Work email - jdike at linux dot intel dot com

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Re: [uml-devel] Regarding Process creation in UML tracing thread mode

[Krishnappa Abhijith-A21204]

Hi Jeff,
		But I was confused with the diagram you described here:
http://user-mode-linux.sourceforge.net/slides/als2000/img4.html

Also from your below response it means that: UML just have a
task_structure maintained....
Also I never saw the UML specific schedule() code in .../arch/um does
UML uses the host schedule itself ?

Regards,
Abhi

-----Original Message-----
From: Jeff Dike [mailto:jdike@addtoit.com] 
Sent: Wednesday, March 21, 2007 7:25 PM
To: Krishnappa Abhijith-A21204
Cc: user-mode-linux-devel@lists.sourceforge.net
Subject: Re: [uml-devel] Regarding Process creation in UML tracing
thread mode

On Wed, Mar 21, 2007 at 07:51:44PM +0800, Krishnappa Abhijith-A21204
wrote:
>              Regarding fork() implementation UML in tracing thread 
> (tt) mode Whenever we call fork in UML the following happens:
>  
> 2 process gets created
> 1 on UML say U_1 and 1 on HOST say H_1

No, one process gets created, in which both the process and the kernel
run.

				Jeff

--
Work email - jdike at linux dot intel dot com

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Re: [uml-devel] Regarding Process creation in UML tracing thread mode

[Jeff Dike]

On Wed, Mar 21, 2007 at 10:11:48PM +0800, Krishnappa Abhijith-A21204 wrote:
> Also from your below response it means that: UML just have a
> task_structure maintained....
> Also I never saw the UML specific schedule() code in .../arch/um does
> UML uses the host schedule itself ?

UML, like any other port, uses the schedule() in kernel/sched.c.  The
UML-specific context switching indirectly uses the host's scheduler
when it switches from one host process to another.  TT mode has the
outgoing process sleeping in a read() on a pipe after waking up the
incoming process from its read by writing a byte down its pipe.

But the host makes no scheduling decisions between UML processes - the
UML scheduler makes the decisions and the host scheduler just decides
when the process chosen by the UML scheduler actually gets some CPU
time.

				Jeff

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Work email - jdike at linux dot intel dot com

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