Re: The effects of WITNESS and INVARIANTS

From: "Robert Watson" <rwatson_at_FreeBSD.ORG>
> On Tue, 24 Feb 2004, Willem Jan Withagen wrote:
> 
> > Just out of curriousity, and 'cause I've got some idle boxes, I started
> > to do some (NFS-)performance testing.  There is still a long way to go,
> > but I've but a first obvious result online running on the local server
> > disk. 
> > 
> > It makes the claims of the effects of WITNESS and INVARIANTS very
> > obvious.  Look especially at the graph for "Sequential block read". 
> > 
> > You might want to have a look at: 
> >     http://withagen.dyndns.org/FreeBSD/nfs-performance/index.html.  Note
> > that no NFS data is included.  I have some Bonnie-NFS data, but need to
> > write accompanying test and conclusions for it. 
> > 
> > Suggestions are more than welcomed. 
> 
> My primary suggestion is "Turn off WITNESS and INVARIANTS when
> benchmarking or for production systems".  We turn them off in releases,
> and once 5.x becomes 5-stable, we'll turn it off by default also. However,
> they're invaluable tools when debugging the development system, so we have
> them on in the development branch by default.  I would encourage people to
> generally run with them turned on unless performance of a system requires
> them to be off, as it really helps the debugging process, as well as
> helping to identify locking problems as the system evolves. 

Hi Robert,

I understand your concern and will take your remark as made here, and put it
in the document as a "Nota Bene"...
And I'll emphasise the fact that the 5-stable fact is the turning corner for
this matter.

--WjW