Re: LWPs and LWKTs, how they relate

["Simon 'corecode' Schubert" <corecode@xxxxxxxxxxxx>]

On 06.10.2005, at 00:14, Alex Burke wrote:
> Firstly, I hope this email is in the correct format.... I am sending 
> from gmail, and have disabled the rich text formatting stuff.

Unfortunately something in the mailway still fucks up the 
base64-encoded mails from gmail...

> I was just wondering, what will be the interaction between LWPs (I saw 
> a commit message indicating we will be implementing these) and LWKTs.

Each LWP has exactly one LWKT associated.  This is the 1:1 part of the 
threading.  Of course there still will be LWKTs that don't have any LWP 
associated (kernel threads).

> Also, in the conext of DragonFlyBSD after this change... what will a 
> "process" entity actually be?

The process entity will still be "struct proc".  This represents the 
process, i.e. vmspace, credentials, open files, alarm timers, signal 
actions (not masks), and stuff like that.

> I notice in a commit mesasage that a mapping of one LWP to one process 
> is currently enforced, will this change?

Yes.  As soon as the kernel is fully aware of lwps and uses them to 
actually access thread-local data (sigmask, accounting statistics) we 
can remove the embedded lwp and allocate a new lwp every time a process 
spawns a new thread.

> What distinguishes a classic process from a LWP? (reading'moden 
> operating systems', i thought a process was something that had 
> executable conext, possibly multiple (i.e. a threaded program), but 
> included all associated file descriptors etc... not sure what this new 
> subdivision does).

That's exactly the division.  A process (struct proc) has a vmspace, 
file descriptors, etc.  Each thread within a process (struct lwp) 
carries that data neccessary for its execution (signal mask and 
attached lwkt being one of the most important things).

So it is:

proc 1 <-> lwp 1 <-> lwkt 1  [single threaded]

proc 2 <-> lwp 2 <-> lwkt 2  [multi threaded]
        \> lwp 3 <-> lwkt 3

                     lwkt 4  [kernel thread]

One proc groups multiple "threads" called struct lwp.

> Hope this question does not seem too stupid.

Not at all!  I will come up with a roadmap in some minutes.

cheers
  simon

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