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 16:26, Jan Beulich wrote:
> > > > On 18.10.13 at 10:14, annie li <annie.li@xxxxxxxxxx> wrote:
> > 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.
> No, the code (on a 32-bit arch) just _can't_ handle jiffies differences
> beyond 2^32, no matter how cleverly you use the respective macros.
> All arithmetic there is done modulo 2^32.
On 32-bit arch, the jiffies difference beyond 2^32 is only in theory, 
and the real value of jiffies would wrap around after 2^32. Then it will 
still be verified by time_in_range_open, the code will either replenish 
the credit or hit the timer soon.
Thanks
Annie

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