Messages in this thread |  | | Date | Tue, 20 Aug 2002 12:06:01 -0500 | From | Oliver Xymoron <> | Subject | Re: [RFC] Improved add_timer_randomness for __CRIS__ (instead of rdtsc()) |
| |
On Tue, Aug 20, 2002 at 06:32:29PM +0200, johan.adolfsson@axis.com wrote: > > From: "Oliver Xymoron" <oxymoron@waste.org> > > On Tue, Aug 20, 2002 at 11:31:10AM +0200, johan.adolfsson@axis.com wrote: > > > The cris architecture don't have any tsc, but it has a couple of > > > timer registers that can be used to get better than jiffie resolution. > > > > > > I set the time to a 40 us resolution counter with a slight > > > "jump" since lower 8 bit only counts from 0 to 249, > > > the patch does not take wrapping of the register into account either > > > to save some cycles, is that a problem or a good thing? > > > > That should be fine. More important is actually scaling the entropy > > count based on the timing granularity of the source. Keyboards and > > mice tend to have a granularity of about 1khz so timestamps better > > than milliseconds 'invent' entropy in the current code. > > The ETRAX chips where the cris architecture is used is typically used in > headless embedded devices connected to a network. Currently I don't think > we use SA_RANDOM anywhere in our device drivers although it would be > nice to be able to use network and other interfaces as entropy/randomness > source (serial, parallel etc.) without to much concerns.
See my recent (lengthy) posts on this subject.
> > > The num is xor:d with the value from 2 timer registers, > > > which in turn contains different fields breifly described below. > > > > > > Does the patch below look sane? > > > > Looks fine, but I think we want to come up with a cleaner scheme of > > having per-arch high-res timestamps. I'd hate to have that grow to > > several pages of ifdefs and not have it available anywhere else. > > Yes, I've seen the discussion before. > Any idea of how such a solution should look like? > Put an inline function or macro in asm/timex.h (?) together with an > ARCH_HAS_RANDOM_TIMESTAMP define?
I don't think we want to make it specific to random. I think we just want to call it hires.
> E.g. like this for i386: > #define ARCH_HAS_RANDOM_TIMESTAMP > #define RANDOM_TIMESTAMP(time, num) do{\ > if ( test_bit(X86_FEATURE_TSC, &boot_cpu_data.x86_capability) ) { \ > __u32 high; \ > rdtsc(time, high); \ > num ^= high; \ > } else { \ > time = jiffies; \ > } \ > }while(0) > > And then in random.c: > ifdef ARCH_HAS_RANDOM_TIMESTAMP > RANDOM_TIMESTAMP(time, num); > #else > time = jiffies; > #endif
Again, too random-specific. And we need a way to get the timescale. Perhaps something like:
speed=get_timestamp_khz; lowbits=get_hires_timestamp();
-- "Love the dolphins," she advised him. "Write by W.A.S.T.E.." - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
|  |