From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Brown Subject: Re: Proposal: Use hi-res clock for file timestamps Date: Thu, 19 Aug 2010 10:52:18 +1000 Message-ID: <20100819105218.7620ec29@notabene> References: <87aaolwar8.fsf@basil.nowhere.org> <20100817174134.GA23176@fieldses.org> <20100817182920.GD18161@basil.fritz.box> <20100817190447.GA28049@fieldses.org> <20100817203941.729830b7@lxorguk.ukuu.org.uk> <20100817192937.GD26609@fieldses.org> <20100818155359.66b9ddb6@notabene> <20100818173203.GC32430@fieldses.org> <0F91AB9D-0E14-4384-ADD6-0A467C3ABFAC@oracle.com> <20100819094136.24fef59b@notabene> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: "J. Bruce Fields" , Alan Cox , "Patrick J. LoPresti" , Andi Kleen , linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel To: Chuck Lever Return-path: In-Reply-To: <20100819094136.24fef59b@notabene> Sender: linux-nfs-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-fsdevel.vger.kernel.org On Thu, 19 Aug 2010 09:41:36 +1000 Neil Brown 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 -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html