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

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Date:	Wed, 16 Oct 2013 23:04:34 +0800
From:	jianhai luan <jianhai.luan@...cle.com>
To:	Wei Liu <wei.liu2@...rix.com>
CC:	annie li <annie.li@...cle.com>, xen-devel@...ts.xenproject.org,
	Ian Campbell <Ian.Campbell@...rix.com>, netdev@...r.kernel.org
Subject: Re: [Xen-devel] DomU's network interface will hung when Dom0 running
 32bit


On 2013-10-16 21:47, Wei Liu wrote:
> On Wed, Oct 16, 2013 at 09:08:03PM +0800, jianhai luan wrote:
> [...]
>>>>>     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.
>>> Or check following to see what the if condition really do,
>>>
>>> ----------expires-------now-------credit----------    is the only
>>> case where we need to add a timer.
>>>
>>> Other cases like following would match the if condition above,
>>> then no timer is added.
>>> ----------expires----------credit------now------
>>> -----now-----expires----------credit----------
>>>
>>> Or we can consider the extreme condition, when the rate control
>>> does not exist, "credit_usec" is zero, and "next_credit" is equal
>>> to "expires". The above if condition would cover all conditions,
>>> and no rate control really happens. If credit_usec is not zero,
>>> the "if condition" would cover the range outside of that from
>>> expires to next_credit.
>>>
>>> Even if "now" is wrapped again into the range from "expires" to
>>> "next_credit", the "next_credit" that is set in __mod_timer is
>>> reasonable value(this can be gotten from credit_usec), and the
>>> timer would be hit soon.
>> Thanks Annie's express, my option is consistent with Annie.
>>
> OK, thanks for the explanation. I think I get the idea.
>
> In any case, could you use !time_in_range / !time_in_range_open instead
> of open coded one-liner? Though I presume one-liner open coding would
> not hurt.

I agree above the suggest. The attachment patch may be better than 
previous patch.

Jason
>
> Wei.


View attachment "0001-xen-netback-pending-timer-only-in-the-range-expire-n.patch" of type "text/plain" (1628 bytes)