Interesting data points. ----- "Steven Jenkins" <[email protected]> wrote:
> On Fri, Jul 29, 2011 at 12:22 PM, Andrew Deason > <[email protected]> wrote: > > On Thu, 28 Jul 2011 10:09:39 -0400 > > Jeffrey Altman <[email protected]> wrote: > > > >> File systems do not copy this information to each other directly. > All > >> metadata is copied through an operating system VFS layer. Are > there > >> any VFS layers that actually provide better than 100ns resolution? > > > > I've been told verbally (informally) that z/OS offers ns-granular > > timestamp information. I can't find documentation confirming that, > but > > I'm not really sure where to look, either. > > > > It's also not strictly true that we always go through a VFS layer, > since > > we could be translating directly to/from NFS, or there could be a > > userspace application that speaks those protocols directly. Going > > through an OS VFS is certainly the vast vast majority of cases, > though. > > > > I'm not saying that means we care, but I believe those are some > cases > > where we would lose precision. > > > > I agree that most accesses are done via the VFS layer. However, > filesystems are starting to appear that have higher resolution time, > and it is only natural for applications to take advantage of this > infromation. > > As an additional example beyond NFSv4 and z/OS, Btrfs, which has > been > shipping with Linux kernels for over a year, defines the following > for > times (i.e., ctime, atime, mtime) > > struct btrfs_timespec { > __le64 sec; > __le32 nsec; > } __attribute__ ((__packed__)); > > Since we are going to the effort now to define hi-resolution time for > OpenAFS, it seems better to do this once, rather than do a > specification for 100ns time resolution now, and another higher > resolution specification in the future which will then leave us with > two high-res times, or a need to do a migration. > > Steven > _______________________________________________ > AFS3-standardization mailing list > [email protected] > http://lists.openafs.org/mailman/listinfo/afs3-standardization -- Matt Benjamin The Linux Box 206 South Fifth Ave. Suite 150 Ann Arbor, MI 48104 http://linuxbox.com tel. 734-761-4689 fax. 734-769-8938 cel. 734-216-5309 _______________________________________________ AFS3-standardization mailing list [email protected] http://lists.openafs.org/mailman/listinfo/afs3-standardization
