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Date:      Thu, 23 Jul 2015 09:09:01 +0100
From:      Mark R V Murray <markm@FreeBSD.org>
To:        Jeff Roberson <jroberson@jroberson.net>
Cc:        src-committers <src-committers@freebsd.org>, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   Re: svn commit: r284959 - in head: . share/man/man4 share/man/man9 sys/conf sys/dev/glxsb sys/dev/hifn sys/dev/random sys/dev/rndtest sys/dev/safe sys/dev/syscons sys/dev/ubsec sys/dev/virtio/random sy...
Message-ID:  <F7404E39-4ADB-4DE3-80C0-633B978BD231@FreeBSD.org>
In-Reply-To: <alpine.BSF.2.20.1507222157170.1071@desktop>
References:  <201506301700.t5UH0jPq001498@svn.freebsd.org> <alpine.BSF.2.20.1507221138360.1071@desktop> <FFAED695-145A-45F5-988D-B843EF5F544B@FreeBSD.org> <alpine.BSF.2.20.1507221249120.1071@desktop> <FFFB06D7-164B-40B3-AFC3-A6630BCF074E@bsdimp.com> <E20B169F-4C8A-4D11-9853-5C2EFC116450@FreeBSD.org> <alpine.BSF.2.20.1507222157170.1071@desktop>

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> On 23 Jul 2015, at 08:59, Jeff Roberson <jroberson@jroberson.net> =
wrote:
>=20
>>=20
>> OK - I?m sold! I?ll make a kernel option defaulting to off. :-)
>=20
> There are other sources that occur less frequently than millions of =
times per-second that may still provide some usefull entropy while being =
less performance critical under normal conditions.

I=E2=80=99m sure there are, and I=E2=80=99m keen to discover more! I=E2=80=
=99m not exactly the worlds best kernel hacker, so I=E2=80=99ll be =
requesting help.

My own crappy benchmark is =E2=80=9Cmake world=E2=80=9D and for that, I =
notice very little. For Video at Ludicrous Speed(=E2=84=A2), I=E2=80=99m =
well prepared to accept otherwise! For crypto purposes, UMA is =
brilliant, though (but that won=E2=80=99t stop me defaulting it to =
=E2=80=9Ccompiled out=E2=80=9D).

> For example, context switches, traps, etc.  I could also imagine =
wiring up a pmc counter to something like cache misses or branch =
mispredicts that would be more difficult to game, especially if the =
counter was cycled irregularly.

Help requested here, please! If you could point out suitable harvesting =
points, I=E2=80=99ll see if the numbers from them look good.

Thanks!

M
--=20
Mark R V Murray




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