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

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Date:	Thu, 17 Oct 2013 17:41:27 +0100
From:	Wei Liu <wei.liu2@...rix.com>
To:	annie li <annie.li@...cle.com>
CC:	Jan Beulich <JBeulich@...e.com>,
	jianhai luan <jianhai.luan@...cle.com>,
	<david.vrabel@...rix.com>, <ian.campbell@...rix.com>,
	<wei.liu2@...rix.com>, <xen-devel@...ts.xenproject.org>,
	<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 12:38:12AM +0800, annie li wrote:
> 
> On 2013-10-17 17:26, Jan Beulich wrote:
> >>Yes, the issue only can be  reproduced in 32-bit Dom0 (Beyond
> >>MAX_ULONG/2 in 64-bit will need long long time)
> >>
> >>I think the gap should be think all environment even now extending 480+.
> >>if now fall in the gap,  one timer will be pending and replenish will be
> >>in time.  Please run the attachment test program.
> >Not sure what this is supposed to tell me. I recognize that there
> >are overflow conditions not handled properly, but (a) I have a
> >hard time thinking of a sensible guest that sits idle for over 240
> >days (host uptime usually isn't even coming close to that due to
> >maintenance requirements) and (b) if there is such a sensible
> >guest, then I can't see why dealing with one being idle for over
> >480 days should be required too.
> >
> 
> If the guest contains multiple NICs, that situation probably happens
> when one NIC keeps idle and others work under load. BTW, how do you
> get the 240?
> 

I think Jan got this number with HZ=100. It take ~240 days for jiffies
to overflow in 32 bit machine when HZ=100.

Wei.

> Thanks
> Annie
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