kernel thread as real threads..

Julian Elischer julian at
Mon Jan 23 16:59:13 PST 2006

David Xu wrote:

> Julian Elischer wrote:
>> John Baldwin wrote:
>>> On Thursday 19 January 2006 21:56, Julian Elischer wrote:
>>>> some progrsss..
>>>> as the first few lines show, it's not quite perfect yet but it's 
>>>> most of
>>>> the way there..
>>>> (Like proc 1 isn't init)
>>> One other note, watch out for the AIO daemons.  They have to be 
>>> kernel procs and not kthreads because they borrow the vmspace of the 
>>> user process when performing AIO on another process' behalf.
>> yeah I found that and the patches account for that.
>> However I would like to suggest that we change the way that aio works..
>> My suggestion is that when a process does AIO, that we "fork a 
>> ksegroup" and attach it to the
>> process, and assign it a (or some) worker thread to do the aio work.  
>> The userland process would
>> be oblivious of the extra (kernel) threads in that kseg and they 
>> would be independently schedulable.
>> They would however automatically have full access to the correct 
>> address space.
> These threads should be invisible to userland debugger, and other code
> current unknown, for example, signal code ? The idea seems simply but we
> may in fact encounter problem, because you inject unknown threads to a

> process. :-)

If the userland doesn't know about them, how would it affect it?
As a kernel thread it wouldn't take part in signals, other than to abort 
when the process exits.
it    WOULD accumulate cpu time for the process.. but that is just fair. 
currently I think that
aio is "free".

Anyhow I'm not ready to try do it now.. As the current patches leave the 
status-quo for aio.

> I still prefer current model, also the aiod threads can be reused for 
> multiple
> processes.

that is both a positive and a negative when it comes to accounting.

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