Messages in this thread | | | Date | Thu, 19 Aug 2010 10:52:18 +1000 | From | Neil Brown <> | Subject | Re: Proposal: Use hi-res clock for file timestamps |
| |
On Thu, 19 Aug 2010 09:41:36 +1000 Neil Brown <neilb@suse.de> wrote:
> So I agree that this is probably more of an issue for directories than for > files, and that implementing it just for directories would be a sensible > first step with lower expected overhead - just my reasoning seems to be a bit > different.
Just to be sure we are on the same page: file_update_time would always refer to current_nfsd_time, but nfsd would only update current_nfsd_time when a directory was examined (and the other conditions were met).
So my current thinking on how this would look - names have been changed:
- global timespec 'current_fs_precise_time' is zeroed when current_kernel_time moves backwards and is protected by a seqlock
- current_fs_time would be now = max(current_kernel_time(), current_fs_precise_time) return timespec_trunc(now, sb->s_time_gran) (with appropriate seqlock protection)
- new function in fs/inode.c get_precise_time(timestamp) cft = current_fs_time() if (timestamp == cft) write_seqlock() if cft == current_fs_precise_time current_fs_precise_time.tv_nsec++ else if cft > current_fs_precise_time current_fs_precise_time = cft write_sequnlock() return timestamp
- nfsd xdr response routine does ts = inode->i_mtime if (S_ISDIR(inode->i_mode)) ts = get_precise_time(ts) xdr_encode_timespec(ts)
get_precise_time() probably needs a bit more subtlety to handle different s_time_gran values and possible races, but I think it is fairly close.
Then if we ever had an xstat or similar that could ask for precise timestamps, it just makes a similar call to get_precise_time. Also if we added code later to use a hires timer on hardware where it was efficient, get_precise_time could test for that and become a no-op
Yes, I should probably turn this into a patch ... maybe another day.
NeilBrown
| |