From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga04.intel.com (mga04.intel.com [192.55.52.120]) by dpdk.org (Postfix) with ESMTP id 425F8A10 for ; Sat, 23 Jul 2016 13:15:31 +0200 (CEST) Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmsmga104.fm.intel.com with ESMTP; 23 Jul 2016 04:15:30 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.28,408,1464678000"; d="scan'208";a="851813192" Received: from irsmsx101.ger.corp.intel.com ([163.33.3.153]) by orsmga003.jf.intel.com with ESMTP; 23 Jul 2016 04:15:30 -0700 Received: from irsmsx105.ger.corp.intel.com ([169.254.7.51]) by IRSMSX101.ger.corp.intel.com ([169.254.1.155]) with mapi id 14.03.0248.002; Sat, 23 Jul 2016 12:15:27 +0100 From: "Ananyev, Konstantin" To: Jerin Jacob CC: Thomas Monjalon , Juhamatti Kuusisaari , "dev@dpdk.org" Thread-Topic: [dpdk-dev] [PATCH] lib: change rte_ring dequeue to guarantee ordering before tail update Thread-Index: AQHR5MEAWScYtg9T2kKIsNyA6C8w66AlsRIAgAAV21D///uYgIAAFI3g Date: Sat, 23 Jul 2016 11:15:27 +0000 Message-ID: <2601191342CEEE43887BDE71AB97725836B812E8@irsmsx105.ger.corp.intel.com> References: <20160715043951.32040-1-juhamatti.kuusisaari@coriant.com> <2601191342CEEE43887BDE71AB97725836B7E32F@irsmsx105.ger.corp.intel.com> <14017551.U6D1dIIx0P@xps13> <20160723060515.GA13747@localhost.localdomain> <20160723093621.GA18376@localhost.localdomain> <2601191342CEEE43887BDE71AB97725836B81292@irsmsx105.ger.corp.intel.com> <20160723103847.GB18376@localhost.localdomain> In-Reply-To: <20160723103847.GB18376@localhost.localdomain> Accept-Language: en-IE, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [163.33.239.180] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Subject: Re: [dpdk-dev] [PATCH] lib: change rte_ring dequeue to guarantee ordering before tail update X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 23 Jul 2016 11:15:31 -0000 > -----Original Message----- > From: Jerin Jacob [mailto:jerin.jacob@caviumnetworks.com] > Sent: Saturday, July 23, 2016 11:39 AM > To: Ananyev, Konstantin > Cc: Thomas Monjalon ; Juhamatti Kuusisaari ; dev@dpdk.org > Subject: Re: [dpdk-dev] [PATCH] lib: change rte_ring dequeue to guarantee= ordering before tail update >=20 > On Sat, Jul 23, 2016 at 10:14:51AM +0000, Ananyev, Konstantin wrote: > > Hi lads, > > > > > On Sat, Jul 23, 2016 at 11:02:33AM +0200, Thomas Monjalon wrote: > > > > 2016-07-23 8:05 GMT+02:00 Jerin Jacob : > > > > > On Thu, Jul 21, 2016 at 11:26:50PM +0200, Thomas Monjalon wrote: > > > > >> > > Consumer queue dequeuing must be guaranteed to be done > > > > >> > > fully before the tail is updated. This is not guaranteed > > > > >> > > with a read barrier, changed to a write barrier just before > > > > >> > > tail update which in > > > practice guarantees correct order of reads and writes. > > > > >> > > > > > > >> > > Signed-off-by: Juhamatti Kuusisaari > > > > >> > > > > > > >> > > > > > >> > Acked-by: Konstantin Ananyev > > > > >> > > > > >> Applied, thanks > > > > > > > > > > There was ongoing discussion on this > > > > > http://dpdk.org/ml/archives/dev/2016-July/044168.html > > > > > > > > Sorry Jerin, I forgot this email. > > > > The problem is that nobody replied to your email and you did not > > > > nack the v2 of this patch. > > > > It's probably my bad. > > I acked the patch before Jerin response, and forgot to reply later. > > > > > > > > > > > This change may not be required as it has the performance impact. > > > > > > > > We need to clearly understand what is the performance impact > > > > (numbers and use cases) on one hand, and is there a real bug fixed > > > > by this patch on the other hand? > > > > > > IHMO, there is no real bug here. rte_smb_rmb() provides the > > > LOAD-STORE barrier to make sure tail pointer WRITE happens only after= prior LOADS. > > > > Yep, from what I read at the link Jerin provided, indeed it seems rte_s= mp_rmb() is enough for the arm arch here... > > For ppc, as I can see both rte_smp_rmb()/rte_smp_wmb() emits the same i= nstruction. > > > > > > > > Thoughts? > > > > Wonder how big is a performance impact? >=20 > With this change we need to wait for addtional STORES to be completed to = local buffer in addtion to LOADS from ring buffers memory. I understand that, just wonder did you see any real performance difference? Probably with ring_perf_autotest/mempool_perf_autotest or something? Konstantin=20 >=20 > > If there is a real one, I suppose we can revert the patch? >=20 > Request to revert this one as their no benifts for other architectures an= d indeed it creates addtional delay in waiting for STORES to complete > in ARM. > Lets do the correct thing by reverting it. >=20 > Jerin >=20 >=20 >=20 > > Konstantin > > > > > > > > > > > > > Please guys make things clear and we'll revert if needed.