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

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Message-ID: <AANLkTi=sOW0Cgci+xX6rRmz+B-is0xb8DoKD350bFJN1@mail.gmail.com>
Date:	Tue, 17 Aug 2010 12:34:58 -0700
From:	"Patrick J. LoPresti" <lopresti@...il.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	"J. Bruce Fields" <bfields@...ldses.org>,
	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 12:39 PM, Alan Cox <alan@...rguk.ukuu.org.uk> wrote:

>        if (time_now == time_last)
>                return { time_last , ++ct };
>        else {
>                ct = 0;
>                time_last = time_now
>                return { time_last , 0 };
>        }
>
> providing it is done with the same 'ct' across the fs and you can't do
> enough ops/second to wrap the nanosecs - which should be fine for now,
> your ordering is still safe is it not ?

Yes, that would work.   Assuming you use atomic counters, else there
is a risk of the visible time ticking backwards.  It seems like a lot
of effort just to avoid having accurate timestamps on your files,
though.

I am having trouble seeing why this is a better idea than a simple
mount option to obtain decent resolution timestamps.  (Not that we
can't have both...)  Is there any objection to the mount option I am
proposing?

For the Nth time, I am willing to produce and test the patch, but not
if there is zero chance of it being accepted.

 - Pat
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