Subject: Re: Issue 90 of the NetBSD CVS Digest is out.
To: Current Users <>
From: Matthias Scheler <>
List: current-users
Date: 02/11/2007 23:03:47
On 11 Feb 2007, at 22:49, Aaron J. Grier wrote:
> the public announcements don't tell me anything other than "ooh,  
> shiny"
> and neglect to tell me why M:N was seemingly abandoned.

I don't know all the details. What I can remember is:
1.) Our M:N implementation never worked properly on multiple CPUs.
2.) It didn't work very well on certain platforms e.g NetBSD-sparc
     and NetBSD-sparc64.

> this seems like quite a large change and it would be nice to know  
> how we
> got here.

Is it really surprising that we got there? Solaris and Linux both  
moved from
M:N to 1:1 because M:N didn't work very well.

One of the problems with M:N in Linux is e.g. that a userland thread  
can be
running on a kernel thread which was previously used to lock a mutex  
by another
userland thread which is currently not running. And if the active  
thread now
tries to lock the same mutex the application will die because of a
recursive mutex entry.

	Kind regards

Matthias Scheler