Change default VFS timestamp precision?

[Warner Losh]

> On Dec 16, 2014, at 11:48 AM, John Baldwin <jhb at freebsd.org> wrote:
> 
> We still ship with vfs.timestamp_precision=0 by default meaning that VFS
> timestamps have a granularity of one second.  It is not unusual on modern
> systems for multiple updates to a file or directory to occur within a single
> second (and thus share the same effective timestamp).  This can break things
> that depend on timestamps to know when something has changed or is stale (such
> as make(1) or NFS clients).  On hardware that has a cheap timecounter, I we
> should use the most-precise timestamps (vfs.timestamp_precision=3).  However,
> I'm less sure of what to do for other cases such as i386/amd64 when not using
> TSC, or on other platforms.  OTOH, perhaps you aren't doing lots of heavy I/O
> access on a system with a slow timecounter (or if you are doing heavy I/O,
> slow timecounter access won't be your bottleneck)?
> 
> I can think of a few options:
> 
> 1) Change vfs.timestamp_precision default to 3 for all systems.
> 
> 2) Only change vfs.timestamp_precision default to 3 for amd64/i386 using an
>    #ifdef.
> 
> 3) Something else?
> 
> What do other folks think?

(1). If there’s a specific kernel / platform that’s slow, we can make it an option
for those kernels.

Warner

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 842 bytes
Desc: Message signed with OpenPGP using GPGMail
URL: <http://lists.freebsd.org/pipermail/freebsd-arch/attachments/20141216/5185027c/attachment.sig>