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

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Message-ID: <1381848632.21901.42.camel@kazak.uk.xensource.com>
Date:	Tue, 15 Oct 2013 15:50:32 +0100
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Wei Liu <wei.liu2@...rix.com>
CC:	jianhai luan <jianhai.luan@...cle.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 Tue, 2013-10-15 at 15:49 +0100, Wei Liu wrote:
> On Tue, Oct 15, 2013 at 10:29:15PM +0800, jianhai luan wrote:
> > 
> > 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
> > 
> > If now is placed in above environment, the result will be correct
> > (Sending package will be not allowed until next_credit).
> 
> No, it is not necessarily correct. Keep in mind that "now" wraps around,
> which is the issue you try to fix. You still have a window to stall your
> frontend.

Remember that time_after_eq is supposed to work even with wraparound
occurring, so long as the two times are less than MAX_LONG/2 apart.

> 
> > * time_after_eq(now, next_credit)  --> false will include two environment:
> >   expires     now   next_credit
> >   -----------time increases this direction ---->
> > 
> > Or
> >   expires      next_credit             next_credit + MAX_LONG/2 now
> >   -----------time increases this direction ---->
> > 
> > 
> > the first environment should be correct to control transmit. the
> > second environment is our included environment.
> > 
> > Jason
> > >
> > >Then it's stuck again. You're merely narrowing the window, not fixing
> > >the real problem.
> > >
> > >Wei.
> > >
> > >>Jason
> > >>>Wei.


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