Getting rid of the static msleep priority boost

[Kirk McKusick]

> From: John Baldwin <jhb at freebsd.org>
> To: Jeff Roberson <jroberson at chesapeake.net>
> Date: Fri, 7 Mar 2008 08:42:37 -0500
> Cc: arch at freebsd.org
> Subject: Re: Getting rid of the static msleep priority boost
> 
> On Friday 07 March 2008 07:16:30 am Jeff Roberson wrote:
> > Hello,
> >
> > I've been studying some problems with recent scheduler improvements that
> > help a lot on some workloads and hurt on others.  I've tracked the problem
> > down to static priority boosts handed out by msleep/cv_broadcastpri.
> > ...
> 
> ...
>
> This change allows the decision on priority boost to be a scheduler
> decision to ignore it (so 4BSD could continue to do what it does now,
> but ULE may ignore it, or ignore certain levels, etc.)
> 
> -- 
> John Baldwin

I strongly agree with John's suggestion. The 4BSD scheduler will continue
to have its historic behavior (which was `tuned' by careful selection of
priority boosts) while more sophisticated schedulers like ULE will be able
to use/ignore the priority boosts based on their better knowledge of system
behavior.

	Kirk McKusick