From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vlad Zolotarov Subject: Re: [PATCH v4] ixgbe_pmd: enforce RS bit on every EOP descriptor for devices newer than 82598 Date: Tue, 27 Oct 2015 21:14:57 +0200 Message-ID: <562FCD31.60508@cloudius-systems.com> References: <1440085070-13989-1-git-send-email-vladz@cloudius-systems.com> <55DAD1C9.3010802@cloudius-systems.com> <1764015.lv7zT9MUyf@xps13> <562FC6D4.8000202@cloudius-systems.com> <2601191342CEEE43887BDE71AB97725836AB5A51@irsmsx105.ger.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: "dev@dpdk.org" , "Kirsher, Jeffrey T" , "Brandeburg, Jesse" To: "Ananyev, Konstantin" , Thomas Monjalon , "Zhang, Helin" Return-path: Received: from mail-wi0-f180.google.com (mail-wi0-f180.google.com [209.85.212.180]) by dpdk.org (Postfix) with ESMTP id C23366787 for ; Tue, 27 Oct 2015 20:14:59 +0100 (CET) Received: by wicll6 with SMTP id ll6so174786862wic.1 for ; Tue, 27 Oct 2015 12:14:59 -0700 (PDT) In-Reply-To: <2601191342CEEE43887BDE71AB97725836AB5A51@irsmsx105.ger.corp.intel.com> List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" On 10/27/15 21:10, Ananyev, Konstantin wrote: > Hi lads, > >> -----Original Message----- >> From: Vlad Zolotarov [mailto:vladz@cloudius-systems.com] >> Sent: Tuesday, October 27, 2015 6:48 PM >> To: Thomas Monjalon; Ananyev, Konstantin; Zhang, Helin >> Cc: dev@dpdk.org; Kirsher, Jeffrey T; Brandeburg, Jesse >> Subject: Re: [dpdk-dev] [PATCH v4] ixgbe_pmd: enforce RS bit on every EOP descriptor for devices newer than 82598 >> >> >> >> On 10/27/15 20:09, Thomas Monjalon wrote: >>> Any Follow-up to this discussion? >>> Should we mark this patch as rejected? >> Hmmm... This patch fixes an obvious spec violation. Why would it be >> rejected? > No I don't think we can reject the patch: > There is a reproducible TX hang on ixgbe PMD on described conditions. > Though, as I explained here: > http://dpdk.org/ml/archives/dev/2015-September/023574.html > Vlad's patch would cause quite a big slowdown. > We are still in the process to get an answer from HW guys are there any > alternatives that will allow to fix the problem and avoid the slowdown. +1 > Konstantin > >>> 2015-08-24 11:11, Vlad Zolotarov: >>>> On 08/20/15 18:37, Vlad Zolotarov wrote: >>>>> According to 82599 and x540 HW specifications RS bit *must* be >>>>> set in the last descriptor of *every* packet. >>>>> >>>>> Before this patch there were 3 types of Tx callbacks that were setting >>>>> RS bit every tx_rs_thresh descriptors. This patch introduces a set of >>>>> new callbacks, one for each type mentioned above, that will set the RS >>>>> bit in every EOP descriptor. >>>>> >>>>> ixgbe_set_tx_function() will set the appropriate Tx callback according >>>>> to the device family. >>>> [+Jesse and Jeff] >>>> >>>> I've started to look at the i40e PMD and it has the same RS bit >>>> deferring logic >>>> as ixgbe PMD has (surprise, surprise!.. ;)). To recall, i40e PMD uses a >>>> descriptor write-back >>>> completion mode. >>>> >>>> From the HW Spec it's unclear if RS bit should be set on *every* descriptor >>>> with EOP bit. However I noticed that Linux driver, before it moved to >>>> HEAD write-back mode, was setting RS >>>> bit on every EOP descriptor. >>>> >>>> So, here is a question to Intel guys: could u, pls., clarify this point? >>>> >>>> Thanks in advance, >>>> vlad >>>