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

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Message-ID: <20100817194504.GF26609@fieldses.org>
Date:	Tue, 17 Aug 2010 15:45:04 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	"Patrick J. LoPresti" <lopresti@...il.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Andi Kleen <andi@...stfloor.org>,
	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 Tue, Aug 17, 2010 at 12:43:10PM -0700, Patrick J. LoPresti wrote:
> On Tue, Aug 17, 2010 at 12:54 PM, Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
> >> Is there any objection to the mount option I am proposing?
> >
> > I have none. I doubt I'd use it as it would be too expensive on system
> > performance for some of my boxes, while having an incrementing value is
> > cheap.
> >
> > I don't see the two as conflicting - in fact the bits you need to do the
> > mount option are the bits you also need to do the counter version as
> > well. One fixes ordering at no real cost, the other adds high res
> > timestamps, both are useful.
> 
> A mount option could also allow a choice of timestamp resolutions:
> 
> Traditional (i.e., fast)
> Alan Cox NFS hack (a tad slower but should fix NFS)
> High-res time (slowest but most accurate)
> 
> I will work on a patch this week (weekend at the latest).

I kind of hate to have mount options that are required for nfs exports
to work correctly; it soon makes things too complicated for users to
realiably get right, so distributions end up setting them, and then we
all end up taking the performance tradeoff anyway.

But a mount-option-based version may at least be useful for further
experiments.

--b.
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