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Date: Tue, 7 Sep 2010 15:14:26 +0300
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Subject: Re: disabling group leader perf_event
From: Pekka Enberg <penberg@kernel.org>
To: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Ingo Molnar <mingo@elte.hu>, Avi Kivity <avi@redhat.com>,
        Pekka Enberg <penberg@cs.helsinki.fi>,
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On Tue, Sep 7, 2010 at 1:57 PM, KOSAKI Motohiro
<kosaki.motohiro@jp.fujitsu.com> wrote:
>> As for the intermediate form, you might want to take a look at Dalvik:
>>
>> http://www.netmite.com/android/mydroid/dalvik/docs/dalvik-bytecode.html
>>
>> and probably ParrotVM bytecode too. The thing to avoid is stack-based
>> instructions like in Java bytecode because although it's easy to write
>> interpreters for them, it makes JIT'ing harder (which needs to convert
>> stack-based representation to register-based) and probably doesn't
>> lend itself well to stack-constrained kernel code.
>
> (offtopic)
>
> Afaik, NetBSD plan to include lua interpreter in kernel. it is optimized embedded environment.
>
> (more offtopic)
>
> in kernel interpreter is needed some concern. 1) restricted stack size (typical userland VM
> often use >100K stack size)  2) restrected memory allocation, especially high order allocation
> often fail. 3) GC often makes unacceptable large lag especially on UP kernel. etc etc
> So, We can't apply rich interpreter (e.g. Dalvik, Parrrot) so easily. I think. personally I prefer
> minimum component.

Yes, we definitely don't want to support memory allocation in the
first stages (if ever). I didn't mean that we should integrate Dalvik
or Parriot but that we should look at their _intermediate code_
("bytecode") as an example what we could design for the kernel.