Re: [Xen-devel] generate random numbers

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

I think the short answer is, Xen does not have a mechanism to collect
true randomness at the moment.  I'm not an expert in random numbers,
so the bitrate doesn't mean anything to me.  A couple of possible
solutions come to mind:
* Use pseudo-random numbers to start out with and test your theories,
while working on getting truly random numbers in.
* Punt the problem to dom0: Have a daemon in dom0 to read /dev/urandom
and "upload" values into a ring read by Xen.  If the ring is empty,
use pseudo-random numbers seeded by old values in the ring (?).
* Add entropy-collection to Xen.
* If interrupted by a timer that's longer than 1ms, just take a TSC
and lop off the lower 10 bits.  If you haven't been interrupted by a
timer, use pseudorandom numbers seeded by the lower 10 bits of the
last TSC.

As I said, I'm not an expert in collecting entropy, so some of these
may be obviously brain-dead ideas.  But it might give you enough to
get started.

 -George

On Fri, Feb 12, 2010 at 8:32 AM, michele.paolino
<michele.paolino@xxxxxxxxxxxxxxx> wrote:
> I need less than 10 bits at rate of 10 milliseconds. With a random number I
> will select the next VCPU to schedule.
>
> Michele
>
> On Fri, Feb 12, 2010 at 2:51 AM, James Harper
> <james.harper@xxxxxxxxxxxxxxxx> wrote:
>>
>> >
>> > Hi!
>> > I am interested in writing a scheduler for Xen for academic purposes.
>> I need
>> > to generate random numbers.
>> > Is it possible to generate random numbers in xen hypervisor
>> developement?If
>> > this is possible, how can I do it?
>> >
>>
>> How many bits do you random numbers need to be?
>>
>> At what rate do you need them? (10/second?, 1000000/second?)
>>
>> Would pseudo-random numbers do? If so, what repeat interval is
>> sufficient?
>>
>> James
>
>
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