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 18:19:40 +0800 Message-ID: <525FB9BC.9010608@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> 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]:38881 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754122Ab3JQKTy (ORCPT ); Thu, 17 Oct 2013 06:19:54 -0400 In-Reply-To: <525FAABE.5080806@citrix.com> Sender: netdev-owner@vger.kernel.org List-ID: 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). I think the two better fixed way is below: - By time_before() to judge if now beyond MAX_ULONG/2 - Add another timer to check and update expire in MAX_ULONG>>2 period. Because second way isn't be verified in practical (need more time to waiting jiffes increase), I chose the first. > > David