netdev - Re: [Xen-devel] [PATCH net] xen-netback: add the scenario which now beyond the range time_after

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Message-ID: <20131018112417.GA20185@zion.uk.xensource.com>
Date:	Fri, 18 Oct 2013 12:24:17 +0100
From:	Wei Liu <wei.liu2@...rix.com>
To:	David Laight <David.Laight@...LAB.COM>
CC:	Jan Beulich <JBeulich@...e.com>, annie li <annie.li@...cle.com>,
	<david.vrabel@...rix.com>, <ian.campbell@...rix.com>,
	<wei.liu2@...rix.com>, <xen-devel@...ts.xenproject.org>,
	jianhai luan <jianhai.luan@...cle.com>,
	<netdev@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH net] xen-netback: add the scenario which now
 beyond the range time_after_eq().

On Fri, Oct 18, 2013 at 09:40:33AM +0100, David Laight wrote:
> > > My understanding is this patch does not simply double the span, it is
> > > just stricter than the original one. Please check my previous comments,
> > > I paste it here.
> > 
> > No, the code (on a 32-bit arch) just _can't_ handle jiffies differences
> > beyond 2^32, no matter how cleverly you use the respective macros.
> > All arithmetic there is done modulo 2^32.
> 
> I haven't followed this discussion very closely but it might be possible
> to arrange that the 'incorrect lack of credit' only occurs for a few
> seconds every time 'jiffies' wraps - instead of half of the time.
> Then you'd have to be extremely unlucky to hit the timing window.
> 

As I understand it, this is the idea of this patch -- to narrow down the
timing window.

Wei.

> 	David
> 
> 
> 
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