Date: Tue, 02 Oct 2012 19:22:40 +0200 From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no> To: Ben Laurie <benl@freebsd.org> Cc: Jonathan Anderson <jonathan.anderson@cl.cam.ac.uk>, Pawel Jakub Dawidek <pjd@freebsd.org>, John Baldwin <jhb@freebsd.org>, freebsd-security@freebsd.org, RW <rwmaillists@googlemail.com>, Mariusz Gromada <mariusz.gromada@gmail.com> Subject: Re: Collecting entropy from device_attach() times. Message-ID: <86y5joiyan.fsf@ds4.des.no> In-Reply-To: <86ipat6n0o.fsf@ds4.des.no> ("Dag-Erling =?utf-8?Q?Sm=C3=B8rg?= =?utf-8?Q?rav=22's?= message of "Tue, 02 Oct 2012 15:07:03 %2B0200") References: <20120918211422.GA1400@garage.freebsd.pl> <20120919231051.4bc5335b@gumby.homeunix.com> <20120920102104.GA1397@garage.freebsd.pl> <201209200758.51924.jhb@freebsd.org> <20120922080323.GA1454@garage.freebsd.pl> <20120922195325.GH1454@garage.freebsd.pl> <505E59DC.7090505@gmail.com> <20120923151706.GN1454@garage.freebsd.pl> <5060D723.6020305@gmail.com> <CAG5KPzxf0Rfufk5K6Jt4e85xc7zXY_B3a2Sq0Uf_uVLHbV-baw@mail.gmail.com> <86r4pqqwnm.fsf@ds4.des.no> <86ipat6n0o.fsf@ds4.des.no>
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Dag-Erling Sm=C3=B8rgrav <des@des.no> writes: > http://people.freebsd.org/~des/attachtimes-text.txz 1) There is a bug in the program - I made a couple of changes which I didn't like but didn't fully revert. The (argc !=3D 0) in main() should actually be (argc =3D=3D 0). 2) I modified the program to create a histogram of the lower bits and looked at that in gnuplot. It was immediately obvious that the distribution is extremely non-uniform. I suspect that this is - at least in part - due to the weird way get_cyclecount() computes the value it returns. We should either rewrite it to return something sensible or nuke it and use binuptime() instead. I uploaded a new tarball with the improved program and the histogram: http://people.freebsd.org/~des/attachtimes-total.txz DES --=20 Dag-Erling Sm=C3=B8rgrav - des@des.no
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