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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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()?

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 




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