High-Precision NFS Timestamps

[Eric Reischer]

I recently upgraded our NFS fileserver to an ext4 filesystem, and since 
then we've been having clock skew warnings from make (3.81).  Because 
the ext3 filesystem that was previously running on the NFS server didn't 
support high-precision timestamps, we didn't have clock skew warnings 
because an hourly cron job kept the clocks in relatively close sync.  
However, since ext4 does support sub-second timestamps, we're getting 
warnings about clock skews on the order of a few milliseconds.  I tried 
adding our target objects to the .LOW_RESOLUTION_TIME target, however 
now we're getting a warning about

make: *** Warning: .LOW_RESOLUTION_TIME file .lib_deps has a high 
resolution time stamp
make:  warning: Clock skew detected.  Your build may be incomplete.

Since asking to have system clocks of NFS clients and servers synced to 
sub-millisecond precision is a bit excessive, is there a way (or feature 
request: could there be a way) to set the threshold for clock skews 
either via a runtime Makefile directive, or an environment variable?  I 
can't see any other way to eliminate these warnings without reverting 
back to ext3 (which isn't happening).  If it's a hard-coded value, there 
should be at least a little room for slop in there (~5 milliseconds?) 
due to network lag, etc.  Even on a point-to-point network, there's 
going to be one-way transit times of a millisecond or two.

Cheers