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

[Xin Li]

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On 8/1/14 8:59 PM, Justin T. Gibbs wrote:
> 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”?

What do you think about D521?  (Alexander suggested similar
implementation).

https://phabric.freebsd.org/D521

Cheers,

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