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

[annie li <annie.li@xxxxxxxxxx>]

On 2013-10-18 15:43, Jan Beulich wrote:
> > > > On 17.10.13 at 18:38, annie li <annie.li@xxxxxxxxxx> wrote:
> > On 2013-10-17 17:26, Jan Beulich wrote:
> > > > Yes, the issue only can be  reproduced in 32-bit Dom0 (Beyond
> > > > MAX_ULONG/2 in 64-bit will need long long time)
> > > >
> > > > I think the gap should be think all environment even now extending 480+.
> > > > if now fall in the gap,  one timer will be pending and replenish will be
> > > > in time.  Please run the attachment test program.
> > > Not sure what this is supposed to tell me. I recognize that there
> > > are overflow conditions not handled properly, but (a) I have a
> > > hard time thinking of a sensible guest that sits idle for over 240
> > > days (host uptime usually isn't even coming close to that due to
> > > maintenance requirements) and (b) if there is such a sensible
> > > guest, then I can't see why dealing with one being idle for over
> > > 480 days should be required too.
> > If the guest contains multiple NICs, that situation probably happens
> > when one NIC keeps idle and others work under load. BTW, how do you get
> > the 240?
> 2^31 / 100 / 60 / 60 / 24
>
> Obviously with HZ=1000 the span would be smaller by a factor
> of 10, which would make it even more clear that doubling the
> span doesn't really help.
My understanding is this patch does not simply double the span, it is 
just stricter than the original one. Please check my previous comments, 
I paste it here.
The main change of this patch is copied here too,
if (!time_in_range_open(now, vif->credit_timeout.expires, next_credit))

comments:

----------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

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel