Messages in this thread | | | Subject | Re: [2.4.17/18pre] VM and swap - it's really unusable | From | Robert Love <> | Date | 14 Jan 2002 15:36:44 -0500 |
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On Mon, 2002-01-14 at 15:22, Oliver Neukum wrote:
> > No, this isn't needed. This same problem would occur without > > preemption. Our semaphores now have locking rules such that we aren't > > going to have blatant priority inversion like this (1 holds A needs B, 2 > > holds B needs A). > > No this is a good old deadlock. > The problem with preemption and SCHED_FIFO is, that due to SCHED_FIFO > you have no guarantee that any task will make any progress at all. > Thus a semaphore could basically be held forever. > That can happen without preemption only if you do something that > might block.
Well, semaphores block. And we have these races right now with SCHED_FIFO tasks. I still contend preempt does not change the nature of the problem and it certainly doesn't introduce a new one.
Robert Love
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