Messages in this thread | | | Subject | Re: [PATCH] Replace completions with semaphores | From | Peter Zijlstra <> | Date | Tue, 15 Apr 2008 10:44:48 +0200 |
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On Tue, 2008-04-15 at 09:17 +0200, Bart Van Assche wrote: > On Tue, Apr 15, 2008 at 8:46 AM, Peter Zijlstra <peterz@infradead.org> wrote: > > > > On Tue, 2008-04-15 at 08:18 +0200, Bart Van Assche wrote: > > > Would it really be a good idea to give a synchronization concept that > > > behaves exactly like a semaphore another name than "semaphore" ? The > > > semaphore concept is well known and is taught in every computer > > > science course. > > > > Are the ramifications wrt priority inversion taught? Is it made clear > > that its hard to validate because there is no clear resource owner? > > > > Afaik, non of these subjects are touched upon in the CS-101 courses and > > that is exactly the problem. So you can say they are not well know, they > > are just widely misunderstood. > > > > And yes, if there are more hand a very few such users it doesn't make > > sense to keep them open coded. > > Regarding semaphores and priority inversion: I have never recommended > the use of semaphores over mutexes, all I recommended is to keep the > name "semaphore" for something that behaves like a semaphore. There > might be better ways to discourage the use of the semaphore API, e.g. > letting the compiler print a warning every time a semaphore function > is called unless one or another #define has been enabled.
That sounds horrible; I really prefer targeted replacements like completions that make it clear what they're supposed to be used for.
> Regarding priority inheritance: does the above mean that you consider > priority inheritance as an optimal solution for realizing real-time > behavior in the kernel ? Are you aware of the fundamental problems > associated with priority inheritance ? These issues are well explained > in Victor Yodaiken's paper "Against priority inheritance". See also > http://www.linuxdevices.com/files/misc/yodaiken-july02.pdf .
Priority inheritance isn't ideal, but comming from a general purpose kernel that wasn't build from scratch to accomodate hard realtime its basically the only option.
Also things like lockdep are a real help to a lot of developers - loads of locking bugs never make it into the kernel because of it.
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