Messages in this thread | | | Date | Fri, 23 Jan 2009 17:55:14 -0800 | From | Mandeep Singh Baines <> | Subject | Re: [PATCH v3] softlockup: remove hung_task_check_count |
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Frédéric Weisbecker (fweisbec@gmail.com) wrote: > 2009/1/23 Ingo Molnar <mingo@elte.hu>: > > > > not sure i like the whole idea of removing the max iterations check. In > > theory if there's a _ton_ of tasks, we could spend a lot of time looping > > there. So it always looked prudent to limit it somewhat. > > > > Which means we can loose several of them. Would it hurt to iterate as > much as possible along the task list, > keeping some care about writers starvation and latency? > BTW I thought about the slow work framework, but I can't retrieve > it.... But this thread has already a slow priority. > > Would it be interesting to provide a way for rwlocks to know if there > is writer waiting for the lock?
Would be cool if that API existed. You could release the CPU and/or lock as soon as either was contended for. You'd have the benefits of fine-grained locking without the overhead of locking and unlocking multiple time.
Currently, there is no bit that can tell you there is a writer waiting. You'd probably need to change the write_lock() implementation at a minimum. Maybe if the first writer left the RW_LOCK_BIAS bit clear and then waited for the readers to leave instead of re-trying? That would actually make write_lock() more efficient for the 1-writer case since you'd only need to spin doing a read in the failure case instead of an atomic_dec and atomic_inc.
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