netdev - Re: DomU's network interface will hung when Dom0 running 32bit

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Message-ID: <525E41CF.7090008@oracle.com>
Date:	Wed, 16 Oct 2013 15:35:43 +0800
From:	jianhai luan <jianhai.luan@...cle.com>
To:	Wei Liu <wei.liu2@...rix.com>
CC:	Ian Campbell <Ian.Campbell@...rix.com>,
	xen-devel@...ts.xenproject.org, netdev@...r.kernel.org,
	ANNIE LI <annie.li@...cle.com>
Subject: Re: DomU's network interface will hung when Dom0 running 32bit


On 2013-10-15 20:58, Wei Liu wrote:
> On Tue, Oct 15, 2013 at 07:26:31PM +0800, jianhai luan wrote:
> [...]
>>>>> Can you propose a patch?
>>>> Because credit_timeout.expire always after jiffies, i judge the
>>>> value over the range of time_after_eq() by time_before(now,
>>>> vif->credit_timeout.expires). please check the patch.
>>> I don't think this really fix the issue for you. You still have chance
>>> that now wraps around and falls between expires and next_credit. In that
>>> case it's stalled again.
>> if time_before(now, vif->credit_timeout.expires) is true, time wrap
>> and do operation. Otherwise time_before(now,
>> vif->credit_timeout.expires) isn't true, now -
>> vif->credit_timeout.expires should be letter than ULONG_MAX/2.
>> Because next_credit large than vif->credit_timeout.expires
>> (next_crdit = vif->credit_timeout.expires +
>> msecs_to_jiffies(vif->credit_usec/1000)), the delta between now and
>> next_credit should be in range of time_after_eq().  So
>> time_after_eq() do correctly judge.
>>
> Not sure I understand you. Consider "now" is placed like this:
>
>     expires   now   next_credit
>     ----time increases this direction--->
>
> * time_after_eq(now, next_credit) -> false
> * time_before(now, expires) -> false
>
> Then it's stuck again. You're merely narrowing the window, not fixing
> the real problem.

The above environment isn't stack again. The netback will pending one 
timer to process the environment.

The attachment program will prove if !(time_after_eq(now, next_credit) 
|| time_before(now, vif->credit_timeout.expires)), now will only be 
placed in  above environment [ expires next_credit),  and the above 
environment will be processed by timer in soon.
>
> Wei.
>
>> Jason
>>> Wei.
Jason.

View attachment "main.c" of type "text/plain" (962 bytes)