Re: Mutex vs semaphores scheduler bug

[Peter Zijlstra]

On Fri, 2009-10-16 at 00:44 +0100, David Howells wrote:
> Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> 
> > The problem appears to be that rwsem doesn't allow lock-stealing
> 
> With good reason.  rwsems can be read or write locked for a long time - so if
> readers can jump the queue on read-locked rwsems, then writer starvation is a
> real possibility.  I carefully implemented it so that it is a strict FIFO to
> avoid certain problems I was having.

Well, it kinda sucks that rwsem is slower than a mutex.

What about allowing writer stealing when the next contending task is a
writer?

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