Date: Wed, 10 Feb 2016 08:20:28 +0100 From: Hans Petter Selasky <hps@selasky.org> To: Ryan Stone <rysto32@gmail.com> Cc: "src-committers@freebsd.org" <src-committers@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>, "svn-src-head@freebsd.org" <svn-src-head@freebsd.org> Subject: Re: svn commit: r294327 - in head/sys: dev/cxgb dev/cxgbe dev/e1000 dev/hyperv/netvsc dev/ixgbe dev/mxge netinet sys Message-ID: <56BAE4BC.9000105@selasky.org> In-Reply-To: <CAFMmRNz3uXim3H3-sGuBUBs45Jy8p260ywothgp4iFkUcnvnEw@mail.gmail.com> References: <201601191533.u0JFXSxf037804@repo.freebsd.org> <CAFMmRNz3uXim3H3-sGuBUBs45Jy8p260ywothgp4iFkUcnvnEw@mail.gmail.com>
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On 01/19/16 17:09, Ryan Stone wrote: > On Tue, Jan 19, 2016 at 10:33 AM, Hans Petter Selasky <hselasky@freebsd.org> > wrote: > >> >> + qsort(lc->lro_mbuf_data, lc->lro_mbuf_count, sizeof(struct mbuf *), >> + &tcp_lro_mbuf_compare_header); >> > > In the worst case, qsort() can take O(n**2) time and consume O(n) stack > space. Is there a DOS concern here? > Hi, Our FreeBSD qsort() routine has been specifically modified to not exhibit the so-called QuickSort worst case behaviour of O(N**2) sorting time. This is not documented in our source code, but here: http://cs.fit.edu/~pkc/classes/writing/samples/bentley93engineering.pdf So I think DOS w.r.t O(N**2) is not a valid consern. Thank you for your input Ryan. BTW: Drew Gallatin has tested our qsort() v.s. my mergesort() and found that: "It looks like mergesort is nearly 2x as expensive. (4.7% vs 2.5%)" See: https://reviews.freebsd.org/D5200 And: https://reviews.freebsd.org/D4994 --HPS
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