Messages in this thread | | | Date | Tue, 15 Apr 2008 09:17:09 +0200 | From | "Bart Van Assche" <> | Subject | Re: [PATCH] Replace completions with semaphores |
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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.
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 .
Bart.
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