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SubjectRe: [Ext-rt-dev] Re: [ANNOUNCE] Linux 2.6 Real Time Kernel
Sven Dietrich wrote:
>>>I think patch size is an issue, but I also think that , eventually, we
>>>should change all spin_lock calls that actually lock a mutex to be more
>>>distinct so it's obvious what is going on. Sven and I both agree that
>>>this should be addressed. Is this a non-issue for you? What does the
>>>community want? I don't find your code or ours acceptable in it's
>>>current form , due to this issue.
>>>With the addition of PREEMPT_REALTIME it looks like you more than
>>>doubled the size of voluntary preempt. I really feel that it should
>>>remain as two distinct patches. They are dependent , but the scope of
>>>the changes are too vast to lump it all together.
>>If there is the tendency to touch the concurrency controls in general
>>all over the kernel, then I would suggest a script driven overhaul of
>>all concurrency controls like spin_locks, mutexes and semaphores to
>>general macros like
>>enter_critical_section(TYPE, &var, &flags, whatever);
>>leave_critical_section(TYPE, &var, flags, whatever);

There is nothing here that can not be done with a macro. Don't really need a
script. The optimizer would drop out unused code...

>>where TYPE might be SPIN_LOCK, SPIN_LOCK_IRQ, MUTEX, PMUTEX or whatever
>>we have and come up with in the future.
>>This could be done in a first step and then it is clearly identifiable
>>and it gives us more flexibility to wrap different implementations and
>>lets us change particular points in a more clear way.
>>I would be willing to provide some scripted conversion aid, if there is
>>enough interest to that. I started with some test files and the results
>>are quite encouraging.
> Ideally we would eventually provide some level of tunability, i.e.
> if you want the spinlocks all the way around it should be possible
> to have that, or one could enable degrees of enhancements,
> expanding on the existing sequence starting with PREEMPT, IRQ_THREADS,
> BKL, MUTEX, etc. In addition to that, once the minim set of spinlocks
> necessary for RT is established, additional layers, corresponding to
> the lock nesting order, could be established, making the "mutex-depth"
> somewhat configurable based on the performance requirements.
> The entire effort would have the side effect of making the locking and
> critical sections more distinct, and reveal soft spots in concurrency
> code, as well as to raise awareness of the code density inside
> critical sections.
> The concept of tunable foreground / background responsiveness,
> based on preemptability of low priority processes comes to mind.
> A lot of folks would probably not mind making UI responsiveness
> a little crisper, others will want the throughput.
> I realize this is an early stage to be looking at it so high end,
> but I think in general this type of script would not be a bad addition
> to the patch kit(s).
> Sven
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George Anzinger
Preemption patch:

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