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

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Message-ID: <5260015C.2030100@citrix.com>
Date:	Thu, 17 Oct 2013 16:25:16 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	jianhai luan <jianhai.luan@...cle.com>
CC:	Wei Liu <wei.liu2@...rix.com>, Jan Beulich <JBeulich@...e.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().

On 17/10/13 16:23, jianhai luan wrote:
> 
> On 2013-10-17 22:06, Wei Liu wrote:
>> On Thu, Oct 17, 2013 at 09:59:30PM +0800, jianhai luan wrote:
>> [...]
>>>>>>> If use time_after_eq64(), expire ,next_credit and other member
>>>>>>> will must
>>>>>>> be u64.
>>>>>> Yes, you'll need to store next_credit as a u64 in vif instead of
>>>>>> calculating it in tx_credit_exceeded from expires (which is only an
>>>>>> unsigned long).
>>>>> I know that.  Even we use u64, time_after_eq()  will also do wrong
>>>>> judge
>>>>> in theory (not in reality because need long long time).
>>>> If jiffies_64 has millisecond resolution that would be more than
>>>> 500,000,000 years.
>>> Yes, I agree the fact.
>>>>> I think the two better fixed way is below:
>>>>>    - By time_before() to judge if now beyond MAX_ULONG/2
>>>> This is broken, so no.
>>> Where is broken?  would you like to help me point it out.
>> I think David means you didn't actually fix the problem. Your solution is
>> merely a workaround.
> 
> I have think  about using u64, but more code need to be modified and
> that is not all.  Key point is how to change the element of struct
> time_list (expires)  and don't affect other thing?

I already suggested a way that didn't require changing the timer
structure -- calculate and store next_credit in advanced.

David
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