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* Esben Nielsen <simlo@phys.au.dk> wrote: > > well, another possibility is that the task got blocked again, and we'll > > continue boosting _the wrong chain_. I.e. we'll add extra priority to > > task(s) that might not deserve it at all (it doesnt own the lock we are > > interested in anymore). > > This can't happen. We are always looking at the first waiter on > task->pi_waiter task->pi_lock held when doing the boosting. If task > has released the lock the entry task->pi_waiter is gone and no > boosting will take place! no, the task got blocked _again_, as part of a _new_ blocking chain, and there's a _new_ PI waiter! How does the two-lock preemptible boosting algorithm ensure that if we are in the middle of boosting a blocking-dependency chain: T1 -> T2 -> ... -> TI -> TI+1 -> ... TN-1 -> TN we are at TI, and we [the task doing the boosting] now get preempted. What prevents TI from being part of a _totally new_ blocking-chain, where the only similarity between the two chains is that TI is in the middle of it: T1' -> T2' -> ... -> TI -> TI+1' -> ... TM-1 -> TM' the only match between the two chains is 'TI'. Now the algorithm will happily walk the wrong boosting chain, and will boost the wrong tasks. Ingo - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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