On Oct 27, 2002 13:13 +0100, Andi Kleen wrote:
> Move time_t members in struct stat to struct timespec and allow subsecond
> timestamps for files. Too big to post on the list, because it edits
> a lot of file systems and drivers in a straight forward way.
>
> This is required for reliable "make" on fast computers.
>
> File systems that support nsec storage are currently: XFS, JFS, NFSv3
> (if the filesystem on the server supports it), VFAT (not quite nanosecond),
> CIFS (unit in 100ns which is above what linux supports), SMBFS (for
> newer servers)
Two notes I might make about this:
1) It would be good if it were possible to select this with a config
option (I don't care which way the default goes), so that people who
don't need/care about the increased resolution don't need the extra
space in their inodes and minor extra overhead. To make this a lot
easier to code, having something akin to the inode_update_time()
which does all of the i_[acm]time updates as appropriate.
2) Updating i_atime based on comparing the nsec timestamp is going to be
a killer. I think AKPM saw dramatic performance improvements when he
changed the code to only do the update once/second, and even though
you are "only" updating the atime if the times are different, in
practise this will be always. Even without the "per superblock interval"
you suggest we should probably only update the atime once a second (I
don't think anything is keyed off such high resolution atimes, unlike
make and mtime/ctime).
3) The fields you are usurping in struct stat are actually there for the
Y2038 problem (when time_t wraps). At least that's what Ted said when
we were looking into nsec times for ext2/3. Granted, we may all be
using 64-bit systems by 2038... I've always thought 64 bits is much
to large for time_t, so we could always use 20 or 30 bits for sub-second
times, and the remaining bits for extending time_t at the high end,
and mask those off for now, but that is a separate issue...
Cheers, Andreas
-- Andreas Dilger http://www-mddsp.enel.ucalgary.ca/People/adilger/ http://sourceforge.net/projects/ext2resize/- 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/
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