From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Burakov, Anatoly" Subject: Re: [PATCH] ring: relax alignment constraint on ring structure Date: Fri, 25 May 2018 15:57:07 +0100 Message-ID: <5b5b3620-7674-86bb-125f-78e4796d2dea@intel.com> References: <20170630142609.6180-1-olivier.matz@6wind.com> <20180403132644.23729-1-olivier.matz@6wind.com> <460fd61f-4346-752b-02c9-5ac952ea5215@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit To: Olivier Matz , dev@dpdk.org, "Ananyev, Konstantin" , "Richardson, Bruce" Return-path: Received: from mga07.intel.com (mga07.intel.com [134.134.136.100]) by dpdk.org (Postfix) with ESMTP id 63FC22BBD for ; Fri, 25 May 2018 16:57:10 +0200 (CEST) In-Reply-To: Content-Language: en-US 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 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, Anatoly