Re: [PATCH] RTC: Add mmap method to rtc character driver

Jim Gettys
2006-07-25T21:39:10Z

Keith's the expert (who wrote the smart scheduler): I'd take a wild ass
guess that 10ms is good enough.

Maybe people can keep him on the cc list this time...
- Jim

On Tue, 2006-07-25 at 14:18 -0700, H. Peter Anvin wrote:
> Jim Gettys wrote:
> > On Tue, 2006-07-25 at 14:04 -0700, H. Peter Anvin wrote:
> >
> >> That's why I'm suggesting adding a cheap, possibly low-res, gettimeofday
> >> virtual system call in case there is no way for the kernel to provide
> >> userspace with a cheap full-resolution gettimeofday. Obviously, if a
> >> high-quality gettimeofday is available, then they can be linked together
> >> by the kernel.
> >
> > Low res is fine: X Timestamps are 1 millisecond values, and wrap after a
> > few hundred days. What we do care about is monotonically increasing
> > values (until it wraps). On machines of the past, this was very
> > convenient; we'd just store a 32 bit value for clients to read, and not
> > bother with locking. I guess these days, you'd at least have to protect
> > the store with a memory barrier, maybe....
> >
> > It was amusing years ago to find toolkit bugs after applications had
> > been up for that long (32 bits of milliseconds)... Yes, there are
> > applications and machines that stay up that long, really there are....
> >
>
> Do you need 1 ms resolution, or is 10 ms good enough?
>
> -hpa
>
--
Jim Gettys
One Laptop Per Child