Subject: RE: [Ext-rt-dev] Re: [ANNOUNCE] Linux 2.6 Real Time Kernel
From: Thomas Gleixner <tglx@linutronix.de>
Reply-To: tglx@linutronix.de
To: Sven Dietrich <sdietrich@mvista.com>
Cc: dwalker@mvista.com, Andrew Morton <akpm@osdl.org>, amakarov@ru.mvista.com,
       Ingo Molnar <mingo@elte.hu>, ext-rt-dev@mvista.com,
       LKML <linux-kernel@vger.kernel.org>
In-Reply-To: <EOEGJOIIAIGENMKBPIAEIEJEDKAA.sdietrich@mvista.com>
References: <EOEGJOIIAIGENMKBPIAEIEJEDKAA.sdietrich@mvista.com>
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Organization: linutronix
Message-Id: <1097613420.19549.105.camel@thomas>
Mime-Version: 1.0
Date: Tue, 12 Oct 2004 22:37:00 +0200
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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 ?

tglx


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