Messages in this thread | | | Date | Sat, 19 Mar 2005 17:31:28 +0100 | From | Ingo Molnar <> | Subject | Re: Real-Time Preemption and RCU |
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* Herbert Xu <herbert@gondor.apana.org.au> wrote:
> Ingo Molnar <mingo@elte.hu> wrote: > > > > i really have no intention to allow multiple readers for rt-mutexes. We > > got away with that so far, and i'd like to keep it so. Imagine 100 > > threads all blocked in the same critical section (holding the read-lock) > > when a highprio writer thread comes around: instant 100x latency to let > > all of them roll forward. The only sane solution is to not allow > > excessive concurrency. (That limits SMP scalability, but there's no > > other choice i can see.) > > What about allowing only as many concurrent readers as there are CPUs?
since a reader may be preempted by a higher prio task, there is no linear relationship between CPU utilization and the number of readers allowed. You could easily end up having all the nr_cpus readers preempted on one CPU. It gets pretty messy.
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