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 17:02, jianhai luan wrote:
> On 2013-10-17 16:26, Jan Beulich wrote:
> > > > > On 16.10.13 at 19:22, Jason Luan <jianhai.luan@xxxxxxxxxx> wrote:
> > > time_after_eq() only works if the delta is < MAX_ULONG/2.
> > >
> > > If netfront sends at a very low rate, the time between subsequent calls
> > > to tx_credit_exceeded() may exceed MAX_ULONG/2 and the test for
> > > timer_after_eq() will be incorrect.  Credit will not be replenished and
> > > the guest may become unable to send (e.g., if prior to the long gap, 
> > > all
> > > credit was exhausted).
> > >
> > > We should add the scenario which now beyond 
> > > next_credit+MAX_UNLONG/2. Because
> > > the fact now must be not before than expire, time_before(now, 
> > > expire) == true
> > > will verify the scenario.
> > >      time_after_eq(now, next_credit) || time_before (now, expire)
> > >      ==
> > >      !time_in_range_open(now, expire, next_credit)
> > So first of all this must be with a 32-bit netback. And the not
> > coverable gap between activity is well over 240 days long. _If_
> > this really needs dealing with, then why is extending this from
> > 240+ to 480+ days sufficient? I.e. why don't you simply
> > change to 64-bit jiffy values, and use time_after_eq64()?
> 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.
Sorry for miss the attachment in previous letter. Please check the 
attachment.
> If use time_after_eq64(), expire ,next_credit and other member will 
> must be u64.
> > Jan
> >
> > > Signed-off-by: Jason Luan <jianhai.luan@xxxxxxxxxx>
> > > ---
> > >   drivers/net/xen-netback/netback.c |    7 +++++--
> > >   1 files changed, 5 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/net/xen-netback/netback.c
> > > b/drivers/net/xen-netback/netback.c
> > > index f3e591c..31eedaf 100644
> > > --- a/drivers/net/xen-netback/netback.c
> > > +++ b/drivers/net/xen-netback/netback.c
> > > @@ -1194,8 +1194,11 @@ static bool tx_credit_exceeded(struct xenvif 
> > > *vif,
> > > unsigned size)
> > >       if (timer_pending(&vif->credit_timeout))
> > >           return true;
> > >   -    /* Passed the point where we can replenish credit? */
> > > -    if (time_after_eq(now, next_credit)) {
> > > +    /* Credit should be replenished when now does not fall into the
> > > +     * range from expires to next_credit, and time_in_range_open()
> > > +     * is used to verify whether this case happens.
> > > +     */
> > > +    if (!time_in_range_open(now, vif->credit_timeout.expires, 
> > > next_credit)) {
> > >           vif->credit_timeout.expires = now;
> > >           tx_add_credit(vif);
> > >       }
> > > --
> > > 1.7.6.5
> > >
> > >
> > > _______________________________________________
> > > Xen-devel mailing list
> > > Xen-devel@xxxxxxxxxxxxx
> > > http://lists.xen.org/xen-devel

Attachment: main.c
Description: Text document

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