Re: [PATCH 4/5] tsc: wire up entropy generation function

[Jarod Wilson <jarod@redhat.com>]

Venkatesh Pallipadi wrote:
> On Mon, Jun 13, 2011 at 3:06 PM, Jarod Wilson<jarod@redhat.com>  wrote:
>> TSC is high enough resolution that we can use its low-order byte to
>> stir new data into the random number generator entropy pool.
>
>  From what I vaguely remember from years past, rdtsc, especially last
> few bits of it are not very good as random number source. As they are
> based on lower bus frequency and a multiplier. May be things have
> changed these days. Adding Peter and Suresh for comments.

Ah, that would definitely be good to know. I *have* enabled debug spew 
on my primary test rig though, and the randomness appears to be quite 
good in the low byte using tsc as the primary clocksource. Its a ~3+ 
year old core 2 duo 2.67GHz system though, so things could easily be 
better or worse with more current systems, and I can't say that I've 
tried it out exhaustively with the cpu at full-bore, which could affect 
things (system is mostly idle, so acpi-cpufreq had the cpu dialed back).

-- 
Jarod Wilson
jarod@redhat.com