Scott Long scottl at
Tue Aug 3 09:44:57 PDT 2004

Evan Dower wrote:
> % uptime
> 9:23AM  up 1 day, 15:42, 6 users, load averages: 0,98 1,19 1,25
> With a recent cvsup (and all the rebuilding and installing involved) I 
> have noticed what seems to be an improvement in stability. I must have 
> missed any postings about it. Any, recent cvsup means about an hour 
> before this:
> % uname -a
> FreeBSD 5.2-CURRENT FreeBSD 5.2-CURRENT #0: Sun 
> Aug  1 16:06:05 PDT 2004     
> root at  i386
> I noticed that my kernel has now started saying (in the dmesg):
> WARNING: Kernel preemption is disabled, expect reduced performance.

I turned off normal preemption a few days ago in order to cover up
the stability problems until the responsible parties (including myself)
get them fixed.  It is just a hack for now.

> Of course, I have WITNESS turned on in my debug kernel so I already 
> expect reduced performance. Is this message suggesting that I put 
> FULL_PREEMPTION in my kernel? I was under the impression that it was 
> only useful for seeing where stuff broke. Is stuff so good now that it 
> will improve performance without significant effect on stability? Or 
> perhaps it is indicating that PREEMPTION is #undef'd? I didn't #undef it 
> so if this is the case it must have been changed upstream.

You likely do not want to turn on FULL_PREEMPTION.  If you want the
old behavior, edit /sys/i386/include/param.h and reenable the
PREEMPTION definition.


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