Re: PATCH: sleeping while holding a lock in _pagebuf_free_bh()::page_buf.c

[Christoph Hellwig <hch@xxxxxxxxxxxxx>]

On Wed, Oct 23, 2002 at 05:17:13AM +0200, Andi Kleen wrote:
> > BTW, what is the purpose of wake_up_sync()?
> 
> wake_up_sync() only wakes up the first process/thread waiting on the
> wait queue. Not all. This is to avoid the 'thundering herd' lock performance
> problem with many waiters when lots of processes get woken up all the time 
> just to discover that there is no work for them yet and go to sleep again.
> But it needs careful auditing of the code if it can really tolerate 
> wake one.

wake_up_sync() is exactly like wake_up() - just that it will never
reschedule to woken up thread.  Both wake_up() and wake_up_sync() never
sleep and wake up just the firt process.


> 
> -Andi
> >  
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