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

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.

If use time_after_eq64(), expire ,next_credit and other member will must be u64.


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
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;

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