Re: [RFC] nanoseconds vs. the epoch

On Wed, 2006-05-31 at 14:49 -0600, Andreas Dilger wrote:
> A preliminary patch for nanosecond timestamps is underway.  I consider it
> useful to take (at least) the top two bits of the ns timestamp as an extension
> to the seconds field, extending the unix epoch on 64-bit systems by (at least)
> 272 years without needing more than a 64-bit timestamp.

I think that's a good idea.

> The unanswered question is whether we want to extend the epoch by some orders
> of magnitude at the expense of resolution in the nanoseconds field?  For
> example, NTFS has 100ns resolution for files and if we bumped the ext3
> granularity to only 8ns we would gain 2176 years in the epoch department.
> 
> The other alternative is to be "happy enough" with the 272-year extension
> for the current 128-byte inodes, keeping 1ns maximum resolution and then
> worry about this when we have a 64-bit inode and allocate a larger field
> for seconds (48 bits is enough for 12M years...).

Put me in the "happy enough" camp.  Without doing the math, I think
Moore's Law will predict a need for finer-than-8ns granularity well
before the current epoch + 272 years arrives.

Shaggy
-- 
David Kleikamp
IBM Linux Technology Center