On Thu, Mar 27, 2014 at 7:54 AM, Torsten Duwe <d...@lst.de> wrote: > On Wed, Mar 26, 2014 at 06:03:37PM -0700, H. Peter Anvin wrote: >> I'm wondering more about the default. We default to 50% for >> arch_get_random_seed, and this is supposed to be the default for in effect >> unverified hwrngs... > > If the default were 0, it would be exactly the old behaviour. > How about that? Plus, driver authors would have to come up > with an estimate on their own. > >> On March 26, 2014 5:50:09 PM PDT, Andy Lutomirski <l...@amacapital.net> >> wrote: >> >> + "current hwrng entropy estimation per mill"); >> > >> >As an electrical engineer (sort of), I can't read this without thinking >> >you're talking about the amount by which the current is derated. For >> >example, a 14-50 electrical outlet is rated to 50 Amps. If you use it >> >continuously for a long time, though, the current is derated to 40 >> >Amps. >> > >> >Shouldn't this be called credit_derating or, even better, >> >credit_per_1000bits? > > That's an awkward name for a parameter.
I don't think it's worse than credit_derating. > >> >Also, "per mill" is just obscure enough that someone might think it >> >means "per million". > > No. I looked it up, as we have the precise term "Promille" in German. > Also in electrical engineering, (imperial :-) PCB design, a mil > is one 1000th of an inch. Per million would surely be named PPM. > I'm not saying that "per mill" is wrong -- I'm just saying it's obscure and may confuse people. >> >Why the check for derating > 0? Paranoid users may want zero credit, >> >but they probably still want the thing to run. > > [...] > >> >ratelimit (heavily), please. > > The kthread will stop once the estimated entropy is above the threshold. > derating=0 will wind up one CPU core to 100%. So it's an elegant way > to disable the whole mechanism. > Sorry, I didn't mean ratelimit the loop. I meant ratelimit the printk. >> >Also, would it make sense to round-robin all hwrngs? Even better: >> >collect entropy from each one and add them to the pool all at once. If >> >so, would it make sense for the derating to be a per-rng parameter. > > Finally, the derating _is_ a per-RNG parameter. I also thought about > mixing already, but first I want to see a machine with more than 1 HWRNG :-) > Any Haswell machine with another hwrng will have two of them. (I'm not sure that the rdrand/rdseed thing registers as an hwrng, but still...) --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
