svn commit: r284297 - in head: cddl/contrib/opensolaris/cmd/lockstat sys/kern sys/sys

[Scott Long]

> On Jun 12, 2015, at 4:01 AM, Andriy Gapon <avg at FreeBSD.org> wrote:
> 
> Author: avg
> Date: Fri Jun 12 10:01:24 2015
> New Revision: 284297
> URL: https://svnweb.freebsd.org/changeset/base/284297
> 
> Log:
>  several lockstat improvements
> 
>  0. For spin events report time spent spinning, not a loop count.
>  While loop count is much easier and cheaper to obtain it is hard
>  to reason about the reported numbers, espcially for adaptive locks
>  where both spinning and sleeping can happen.
>  So, it's better to compare apples and apples.
> 

This causes spinning to be exceptionally more expensive just by having
KDTRACE_HOOKS enabled, whether or not Dtrace is actually in use.  It
makes it undesirable to deploy with Dtrace by default since it impacts
performance.  Is there a way to make the expensive collection optional,
or only enable when dtrace is using the lockstat module?  Also have you
seen the other recent performance complaint related to this commit?

Thanks,
Scott