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Date: Wed, 23 Oct 2013 17:07:28 +0100 From: "Jan Beulich" <jbeulich@...e.com> To: <David.Laight@...LAB.COM>, <wei.liu2@...rix.com>, <jianhai.luan@...cle.com> Cc: <david.vrabel@...rix.com>, <ian.campbell@...rix.com>, <xen-devel@...ts.xenproject.org>, <annie.li@...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(). >>> jianhai luan <jianhai.luan@...cle.com> 10/23/13 10:02 AM >>> >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. As said before - I disagree (reducing a timing window is never a solution, only eliminating it is), and I pointed at the alternative (using 64-bit calculations) before. Jan -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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