On Thu, 2009-07-16 at 09:58 +0200, Peter Zijlstra wrote: > > Again, I don't think that either PP or PI is appropriate for use > > in a (SMP) kernel. For non-blocking locks, the current > > no-preeemption spinlock mechanism works. For higher-level > > (blocking) locks, I'm attracted to Jim Anderson's model of > > non-preemptable critical sections, combined with FIFO queue > > service. > But, if I remember well how FMLP works, there is not that much difference between them two... I mean, if you, at any (kernel|user) level define a short critical section, this is protected by a non-preemptive FIFO "queue lock", which is how Linux implements --at least on x86-- spinlocks! :-O Also, I'm not sure I can find in the FMLP paper information about the possibility of a task to suspend itself (e.g., I/O completion) while holding a short lock... I assume this is not recommended, but may be wrong, and, in that case, I hope Prof. Anderson and Bjorn will excuse and correct me. :-) On the other hand, if with "blocking locks" you intended the long ones, I think they hare dealt right with suspension and priority inheritance, even in there. > Right, so there's two points here I think: > > A) making most locks preemptible > B) adding PI to all preemptible locks > > I think that we can all agree that if you do A, B makes heaps of sense, > right? > I don't know about all, but I do... I hope I'm not offending anyone saying that I like priority inheritance!! :-P > Of course, when the decreased period is still sufficient for the > application at hand, the non-preemptible case allows for better > analysis. > Sure! I am impressed as well by the amazing results approaches like the FMLP give in term of schedulabiulity analysis, and think a little bit of spinning would not hurt that much, but not to the point of moving all the locking to spinlocks. :-) Regards, Dario -- <<This happens because I choose it to happen!>> (Raistlin Majere) ---------------------------------------------------------------------- Dario Faggioli, ReTiS Lab, Scuola Superiore Sant'Anna, Pisa (Italy) http://blog.linux.it/raistlin / raistlin@xxxxxxxxx / dario.faggioli@xxxxxxxxxx
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