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    SubjectRE: [Ext-rt-dev] Re: [ANNOUNCE] Linux 2.6 Real Time Kernel
    On Tue, 2004-10-12 at 22:31, 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);
    > >
    > > 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.

    Yup, and having a unique identifiable thing for all that stuff in the
    code would make life easier for coders and for people who want to
    experiment and change things.

    > 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).

    Ok, will try to make it work on more than two files and two patterns.

    Any preferences on scripting language ?


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