Messages in this thread | | | From | (Oliver Neukum) | Subject | Re: [2.4.17/18pre] VM and swap - it's really unusable | Date | Tue, 15 Jan 2002 09:32:17 +0100 |
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On Tuesday 15 January 2002 08:10, george anzinger wrote:
> Yes, this is classic priority inversion. It is here now, today with > semaphors which are held by code that blocks. If the code doesn't > block, why not use a spin lock? If it does, well the problem is here
Because eg. other code that holds the semaphore needs to sleep
> now. I suppose we could set a preempt disable around a semaphore if it > makes you feel better. It doesn't fix the problem if the task blocks
It would make me feel better, but it would defeat the purpose. There's a lot of code holding semaphores.
> AND it is legal to block while holding a preemption lock.
But it's easier to fix. If you can preempt only by explicitely sleeping, you can beat priority invasion by changing basically only wake_up. If you can be preempted at random, you need to know who holds a semaphore.
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