From owner-svn-src-all@FreeBSD.ORG  Sat Aug  2 03:59:17 2014
Return-Path: <owner-svn-src-all@FreeBSD.ORG>
Delivered-To: svn-src-all@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits))
 (No client certificate requested)
 by hub.freebsd.org (Postfix) with ESMTPS id 086B1237;
 Sat,  2 Aug 2014 03:59:17 +0000 (UTC)
Received: from aslan.scsiguy.com (mail.scsiguy.com [70.89.174.89])
 (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
 (Client did not present a certificate)
 by mx1.freebsd.org (Postfix) with ESMTPS id CC2442227;
 Sat,  2 Aug 2014 03:59:15 +0000 (UTC)
Received: from [192.168.0.61] (jt-mbp.home.scsiguy.org [192.168.0.61])
 (authenticated bits=0)
 by aslan.scsiguy.com (8.14.8/8.14.8) with ESMTP id s723x6ju016932
 (version=TLSv1/SSLv3 cipher=AES128-SHA bits=128 verify=NO);
 Fri, 1 Aug 2014 21:59:09 -0600 (MDT)
 (envelope-from gibbs@scsiguy.com)
Content-Type: text/plain; charset=windows-1252
Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\))
Subject: Re: svn commit: r269404 - head/sys/cddl/compat/opensolaris/sys
From: "Justin T. Gibbs" <gibbs@scsiguy.com>
In-Reply-To: <201408012233.s71MXNIx051919@svn.freebsd.org>
Date: Fri, 1 Aug 2014 21:59:06 -0600
Content-Transfer-Encoding: quoted-printable
Message-Id: <57D656EF-5D6B-428B-9DCE-7FA360B1407F@scsiguy.com>
References: <201408012233.s71MXNIx051919@svn.freebsd.org>
To: Xin LI <delphij@freebsd.org>
X-Mailer: Apple Mail (2.1878.6)
Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org,
 src-committers@freebsd.org
X-BeenThere: svn-src-all@freebsd.org
X-Mailman-Version: 2.1.18
Precedence: list
List-Id: "SVN commit messages for the entire src tree \(except for &quot;
 user&quot; and &quot; projects&quot; \)" <svn-src-all.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/options/svn-src-all>,
 <mailto:svn-src-all-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/svn-src-all/>
List-Post: <mailto:svn-src-all@freebsd.org>
List-Help: <mailto:svn-src-all-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/svn-src-all>,
 <mailto:svn-src-all-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Sat, 02 Aug 2014 03:59:17 -0000

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

> Author: delphij
> Date: Fri Aug  1 22:33:23 2014
> New Revision: 269404
> URL: http://svnweb.freebsd.org/changeset/base/269404
>=20
> 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.
>=20
>  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:
>=20
>  	panic: avl_find() succeeded inside avl_add()

I don=92t 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=92t we just use a PCPU counter and =
tag the dbufs with "CPU# << 48 | PCPU_counter=94?

=97
Justin=