Messages in this thread | | | Date | Thu, 14 Oct 2004 09:18:10 +0200 | From | Ingo Molnar <> | Subject | Re: [ANNOUNCE] Linux 2.6 Real Time Kernel |
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* Dipankar Sarma <dipankar@in.ibm.com> wrote:
> On Tue, Oct 12, 2004 at 07:50:29AM +0200, Ingo Molnar wrote: > > > > regarding RCU serialization - i think that is the way to go - i dont > > think there is any sensible way to extend RCU to a fully preempted > > model, RCU is all about per-CPU-ness and per-CPU-ness is quite limited > > in a fully preemptible model. > > It seems that way to me too. Long ago I implemented preemptible RCU, > but did not follow it through because I believed it was not a good > idea. The original patch is here : > > http://www.uwsg.iu.edu/hypermail/linux/kernel/0205.1/0026.html
interesting!
> This allows read-side critical sections of RCU to be preempted. It > will take a bit of work to re-use it in RCU as of now, but I don't > think it makes sense to do so. [...]
note that meanwhile i have implemented another variant:
http://marc.theaimsgroup.com/?l=linux-kernel&m=109771365907797&w=2
i dont think this will be the final interface (the _rt postfix is stupid, it should probably be _spin?), but i think this is roughly the structure of how to attack it - a minimal extension to the RCU APIs to allow for serialization. What do you think about this particular approach?
> [...] My primary concern is DoS/OOM situation due to preempted tasks > holding up RCU.
in the serialization solution in -U0 it would be possible to immediately free the RCU entries and hence have no DoS/OOM situation - although the -U0 patch does not do this yet.
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