Re: [Xen-devel] [PATCH net] xen-netback: add the scenario which now beyond the range time_after_eq().

[jianhai luan <jianhai.luan@xxxxxxxxxx>]

On 2013-10-17 23:25, David Vrabel wrote:
> 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.
I think that  modify next_credit only  will not fix the issue. please 
think about:
  - If jiffies have beyond 32 bit. i assume expire  is 0, jiffies_64 
is  0x1000000ff.
    next_credit = 0 +  <always 32-bit value >

    time_after_eq64(jiffies_64, next_credit ) will always true. 
replenish will always do, rate control will lost their function.
Jason
> David

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