Date: Fri, 1 Aug 2014 21:59:06 -0600 From: "Justin T. Gibbs" <gibbs@scsiguy.com> To: Xin LI <delphij@freebsd.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r269404 - head/sys/cddl/compat/opensolaris/sys Message-ID: <57D656EF-5D6B-428B-9DCE-7FA360B1407F@scsiguy.com> In-Reply-To: <201408012233.s71MXNIx051919@svn.freebsd.org> References: <201408012233.s71MXNIx051919@svn.freebsd.org>
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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 > > 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”? — Justinhelp
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