From: Nikita Danilov <nikita@clusterfs.com>
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Date: Thu, 26 Jan 2006 13:50:12 +0300
To: Helge Hafting <helge.hafting@aitel.hist.no>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, hancockr@shaw.ca
Subject: Re: sched_yield() makes OpenLDAP slow
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	<43D8889E.3020907@aitel.hist.no>
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Helge Hafting writes:

[...]

 > 
 > >nothing says that it can't call pthread_mutex_lock and re-acquire the mutex
 > >before any other thread gets around to getting it.
 > >  
 > >
 > Wrong.
 > The spec says that the mutex must be given to a waiter (if any) at the
 > moment of release.  The waiter don't have to be scheduled at that
 > point, it may keep sleeping with its freshly unlocked mutex.  So the
 > unlocking thread may continue - but if it tries to reaquire the mutex
 > it will find the mutex taken and go to sleep at that point. Then other

You just described a convoy formation: a phenomenon that all reasonable
mutex implementation try to avoid at all costs. If that's what standard
prescribes---the standard has to be amended.

 > 
 > Helge Hafting

Nikita.
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