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Date: Sat, 7 Dec 1996 16:05:47 +0900 (JST)
From: Michael Hancock <michaelh@cet.co.jp>
To: Bakul Shah <bakul@plexuscom.com>
cc: Terry Lambert <terry@lambert.org>, freebsd-hackers@freebsd.org
Subject: Re: clone()/rfork()/threads (Re: Inferno for FreeBSD) 
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On Fri, 6 Dec 1996, Bakul Shah wrote:

> > > scheduling (and appropriately deal with priority inversion) are not
> > > easy.
> > 
> > Heh.  "locking nodes in a directed acylic graph representing a lock
> > heirarchy" will address the priority inversion handily -- assuming
> 
> I was talking about scheduling realtime threads on an MP system,
> running at different priority levels but which may want to share
> objects.  When a high prio. thread has to wait because a low
> priority thread holds a lock it wants, we have priority inversion.
> I don't think fair scheduling is easy when you consider these
> issues.

Terry is talking about a global policy for detecting priority inversion
whereas you are probably talking about a local policy, priority lending.

Priority lending is where lower priority thread holds a lock that a higher
priority thread wants, so the higher priority thread lends its priority
to the lower priority thread to prevent it from being preempted by another
high priority thread that doesn't need the object.

Priority lending is easier for me to understand.  On the other hand maybe
the difference is like the difference between 100VG and 100BT.

Regards,


Mike Hancock