Date: Tue, 25 Sep 2012 17:13:00 -0400 From: John Baldwin <jhb@freebsd.org> To: Mariusz Gromada <mariusz.gromada@gmail.com> Cc: Ben Laurie <benl@freebsd.org>, freebsd-security@freebsd.org, RW <rwmaillists@googlemail.com>, Jonathan Anderson <jonathan.anderson@cl.cam.ac.uk>, Pawel Jakub Dawidek <pjd@freebsd.org> Subject: Re: Collecting entropy from device_attach() times. Message-ID: <201209251713.00800.jhb@freebsd.org> In-Reply-To: <50620E8E.9020501@gmail.com> References: <20120918211422.GA1400@garage.freebsd.pl> <CAG5KPzz3ehKm%2BBN_0MCYfcRFkYxKzFLSTTFEpsJg3kK0BTvChQ@mail.gmail.com> <50620E8E.9020501@gmail.com>
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On Tuesday, September 25, 2012 4:05:34 pm Mariusz Gromada wrote:
> Our task is to check if there are any autocorrelations in the X(w,t)
> process, which means checking if there are any dependencies between
> random variables X(w,t1) and X(w,t2) where t1 < t2.
Just to state an obvious fact (not sure how that impacts your analysis
though): There are, of course, many dependencies among device attach routines
since your total time for the attach routine for a bus is going to include all
of the time it takes for attach to run on all of the child devices. That is,
pci0's attach time includes the attach time of all of it's descendant devices,
and a given leaf node's attach time will be accounted for in the attach time
of all of its parent nodes up to the root. For example:
nexus0
acpi0
pcib0
pci0
ehci0
usbus0
uhub0
uhub3
uhub4
ukbd0
In this portion of my desktop's device tree, all of the devices listed will
include the time of ukbd0's attach in their respective attach times.
--
John Baldwin
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