linux-kernel - Re: Proposal: Use hi-res clock for file timestamps

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Message-ID: <20100818185354.GB6567@basil.fritz.box>
Date:	Wed, 18 Aug 2010 20:53:54 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	"Patrick J. LoPresti" <lopresti@...il.com>,
	linux-fsdevel@...r.kernel.org, linux-nfs@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Proposal: Use hi-res clock for file timestamps

On Wed, Aug 18, 2010 at 07:20:58PM +0100, David Woodhouse wrote:
> On Tue, 2010-08-17 at 20:29 +0200, Andi Kleen wrote:
> > 
> > >       - Increment mtime by a nanosecond when necessary.  
> > 
> > You cannot be more precise than the backing file system: this causes
> > non monotonity when the inodes are flushed (has happened in the past)
> 
> Um, can't you? You can't *store* timestamps which are more precise, but
> they can be in cache can't they?

No you can't. The initial implementation did that and it broke someone's
make. After that the VFS was fixed to never be precise than the backing
file system.

-Andi
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