From mboxrd@z Thu Jan 1 00:00:00 1970 From: jianhai luan Subject: Re: [Xen-devel] [PATCH net] xen-netback: add the scenario which now beyond the range time_after_eq(). Date: Thu, 17 Oct 2013 21:59:30 +0800 Message-ID: <525FED42.4040608@oracle.com> References: <1381944167-24918-1-git-send-email-jianhai.luan@oracle.com> <525FBB4F02000078000FBB30@nat28.tlf.novell.com> <525FA79F.8060601@oracle.com> <525FAABE.5080806@citrix.com> <525FB9BC.9010608@oracle.com> <525FBC7F.9040800@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Jan Beulich , ian.campbell@citrix.com, wei.liu2@citrix.com, xen-devel@lists.xenproject.org, annie.li@oracle.com, netdev@vger.kernel.org To: David Vrabel Return-path: Received: from aserp1040.oracle.com ([141.146.126.69]:36712 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756499Ab3JQN7r (ORCPT ); Thu, 17 Oct 2013 09:59:47 -0400 In-Reply-To: <525FBC7F.9040800@citrix.com> Sender: netdev-owner@vger.kernel.org List-ID: On 2013-10-17 18:31, David Vrabel wrote: > On 17/10/13 11:19, jianhai luan wrote: >> On 2013-10-17 17:15, David Vrabel wrote: >>> On 17/10/13 10:02, jianhai luan wrote: >>>> On 2013-10-17 16:26, Jan Beulich wrote: >>>>>>>> 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()? >>>> 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. >>> Yes, you'll need to store next_credit as a u64 in vif instead of >>> calculating it in tx_credit_exceeded from expires (which is only an >>> unsigned long). >> I know that. Even we use u64, time_after_eq() will also do wrong judge >> in theory (not in reality because need long long time). > If jiffies_64 has millisecond resolution that would be more than > 500,000,000 years. Yes, I agree the fact. > >> I think the two better fixed way is below: >> - By time_before() to judge if now beyond MAX_ULONG/2 > This is broken, so no. Where is broken? would you like to help me point it out. > > David