From mboxrd@z Thu Jan 1 00:00:00 1970 From: Olivier Matz Subject: Re: [PATCH] ring: relax alignment constraint on ring structure Date: Fri, 25 May 2018 17:17:48 +0200 Message-ID: <20180525151748.z6vbvbbbbs3gzcv3@neon> References: <20170630142609.6180-1-olivier.matz@6wind.com> <20180403132644.23729-1-olivier.matz@6wind.com> <460fd61f-4346-752b-02c9-5ac952ea5215@intel.com> <5b5b3620-7674-86bb-125f-78e4796d2dea@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Cc: dev@dpdk.org, "Ananyev, Konstantin" , "Richardson, Bruce" To: "Burakov, Anatoly" Return-path: Received: from mail.droids-corp.org (zoll.droids-corp.org [94.23.50.67]) by dpdk.org (Postfix) with ESMTP id 0865514E8 for ; Fri, 25 May 2018 17:17:53 +0200 (CEST) Content-Disposition: inline In-Reply-To: <5b5b3620-7674-86bb-125f-78e4796d2dea@intel.com> List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" On Fri, May 25, 2018 at 03:57:07PM +0100, Burakov, Anatoly wrote: > On 25-May-18 1:18 PM, Burakov, Anatoly wrote: > > On 25-May-18 11:59 AM, Burakov, Anatoly wrote: > > > On 03-Apr-18 2:26 PM, Olivier Matz wrote: > > > > The initial objective of > > > > commit d9f0d3a1ffd4 ("ring: remove split cacheline build setting") > > > > was to add an empty cache line betwee, the producer and consumer > > > > data (on platform with cache line size = 64B), preventing from > > > > having them on adjacent cache lines. > > > > > > > > Following discussion on the mailing list, it appears that this > > > > also imposes an alignment constraint that is not required. > > > > > > > > This patch removes the extra alignment constraint and adds the > > > > empty cache lines using padding fields in the structure. The > > > > size of rte_ring structure and the offset of the fields remain > > > > the same on platforms with cache line size = 64B: > > > > > > > >    rte_ring = 384 > > > >    rte_ring.name = 0 > > > >    rte_ring.flags = 32 > > > >    rte_ring.memzone = 40 > > > >    rte_ring.size = 48 > > > >    rte_ring.mask = 52 > > > >    rte_ring.prod = 128 > > > >    rte_ring.cons = 256 > > > > > > > > But it has an impact on platform where cache line size is 128B: > > > > > > > >    rte_ring = 384        -> 768 > > > >    rte_ring.name = 0 > > > >    rte_ring.flags = 32 > > > >    rte_ring.memzone = 40 > > > >    rte_ring.size = 48 > > > >    rte_ring.mask = 52 > > > >    rte_ring.prod = 128   -> 256 > > > >    rte_ring.cons = 256   -> 512 > > > > > > > > Link: http://dpdk.org/dev/patchwork/patch/25039/ > > > > Suggested-by: Konstantin Ananyev > > > > Signed-off-by: Olivier Matz > > > > --- > > > > > > This patch causes eal_flags_autotest to hang on FreeBSD. Root cause > > > at this time is unknown, but this is a weird one - the test seems to > > > hang while doing read() in bsd/eal_thread.c:59. Reverting this patch > > > on top of rc5 results in eal_flags_autotest passing. > > > > > > > Further investigation shows that for some reason, if Enter is pressed > > while the test is seemingly "hung", it continues and passes. Or rather, > > it hangs on one test, and if Enter is pressed, it finishes that test and > > hangs on another, after which pressing Enter again will result in test > > succeeding. Weird... > > > > This patch is OK, the problem is in the test :) With this patch, it > apparently blew up in just the right way, but really, the EAL flags autotest > is wrong on FreeBSD because it launches primary processes with '--no-shconf' > option, which corrupt main process's memory. For some reason this only began > manifesting with this patch. Thanks for the analysis, I was also a bit puzzled by the impact... Olivier