From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Jan Beulich" Subject: Re: [Xen-devel] [PATCH net] xen-netback: add the scenario which now beyond the range time_after_eq(). Date: Thu, 17 Oct 2013 09:26:23 +0100 Message-ID: <525FBB4F02000078000FBB30@nat28.tlf.novell.com> References: <1381944167-24918-1-git-send-email-jianhai.luan@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Cc: , , , , , To: "Jason Luan" Return-path: Received: from nat28.tlf.novell.com ([130.57.49.28]:41238 "EHLO nat28.tlf.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751124Ab3JQI03 convert rfc822-to-8bit (ORCPT ); Thu, 17 Oct 2013 04:26:29 -0400 In-Reply-To: <1381944167-24918-1-git-send-email-jianhai.luan@oracle.com> Content-Disposition: inline Sender: netdev-owner@vger.kernel.org List-ID: >>> On 16.10.13 at 19:22, Jason Luan 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 > --- > 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@lists.xen.org > http://lists.xen.org/xen-devel