svn commit: r269404 - head/sys/cddl/compat/opensolaris/sys

[Justin T. Gibbs]

On Aug 1, 2014, at 4:33 PM, Xin LI <delphij at freebsd.org> wrote:

> Author: delphij
> Date: Fri Aug  1 22:33:23 2014
> New Revision: 269404
> URL: http://svnweb.freebsd.org/changeset/base/269404
> 
> Log:
>  Split gethrtime() and gethrtime_waitfree() and make the former use
>  nanouptime() instead of getnanouptime().  nanouptime(9) provides more
>  precise result at expense of being slower.
> 
>  In r269223, gethrtime() is used as creation time of dbuf, which in turn
>  acts as portion of lookup key to maintain AVL invariant where there can
>  not be duplicate items.  Before this change, gethrtime() have preferred
>  better execution time by sacrificing precision, which may lead to panic
>  on busy systems with:
> 
>  	panic: avl_find() succeeded inside avl_add()

I don’t believe that r269223 requires a temporal ordering of the dbufs in the AVL, just unique entries.  So why use an expensive operation like getting high resolution time?  Can’t we just use a PCPU counter and tag the dbufs with "CPU# << 48 | PCPU_counter”?

—
Justin