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

H. Peter Anvin
2006-07-25T21:20:30Z

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