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

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Message-ID: <52678286.6000802@oracle.com>
Date:	Wed, 23 Oct 2013 16:02:14 +0800
From:	jianhai luan <jianhai.luan@...cle.com>
To:	Wei Liu <wei.liu2@...rix.com>,
	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,
	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 2013-10-18 19:24, Wei Liu wrote:
> 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.
Jan,  do you agree the idea or have better suggestion to me.

Thanks,
Jason
>
> Wei.
>
>> 	David
>>
>>
>>
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