From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.droids-corp.org (zoll.droids-corp.org [94.23.50.67]) by dpdk.org (Postfix) with ESMTP id EF3A75F16; Mon, 5 Nov 2018 10:44:54 +0100 (CET) Received: from rsa59-2-82-233-193-189.fbx.proxad.net ([82.233.193.189] helo=droids-corp.org) by mail.droids-corp.org with esmtpsa (TLS1.0:RSA_AES_256_CBC_SHA1:256) (Exim 4.89) (envelope-from ) id 1gJbST-0003lr-Ho; Mon, 05 Nov 2018 10:46:11 +0100 Received: by droids-corp.org (sSMTP sendmail emulation); Mon, 05 Nov 2018 10:44:45 +0100 Date: Mon, 5 Nov 2018 10:44:45 +0100 From: Olivier Matz To: "Gavin Hu (Arm Technology China)" Cc: Bruce Richardson , "dev@dpdk.org" , "thomas@monjalon.net" , "stephen@networkplumber.org" , "chaozhu@linux.vnet.ibm.com" , "konstantin.ananyev@intel.com" , "jerin.jacob@caviumnetworks.com" , Honnappa Nagarahalli , "stable@dpdk.org" Message-ID: <20181105094445.oc36ksxstg56ztkc@platinum> References: <1541066031-29125-1-git-send-email-gavin.hu@arm.com> <1541157688-40012-3-git-send-email-gavin.hu@arm.com> <20181102114344.GA13324@bricha3-MOBL.ger.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) Subject: Re: [dpdk-stable] [PATCH v5 2/2] ring: move the atomic load of head above the loop X-BeenThere: stable@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches for DPDK stable branches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 05 Nov 2018 09:44:55 -0000 Hi, On Sat, Nov 03, 2018 at 01:19:29AM +0000, Gavin Hu (Arm Technology China) wrote: > > > > -----Original Message----- > > From: Bruce Richardson > > Sent: Friday, November 2, 2018 7:44 PM > > To: Gavin Hu (Arm Technology China) > > Cc: dev@dpdk.org; thomas@monjalon.net; stephen@networkplumber.org; > > olivier.matz@6wind.com; chaozhu@linux.vnet.ibm.com; > > konstantin.ananyev@intel.com; jerin.jacob@caviumnetworks.com; > > Honnappa Nagarahalli ; stable@dpdk.org > > Subject: Re: [PATCH v5 2/2] ring: move the atomic load of head above the > > loop > > > > On Fri, Nov 02, 2018 at 07:21:28PM +0800, Gavin Hu wrote: > > > In __rte_ring_move_prod_head, move the __atomic_load_n up and out > > of > > > the do {} while loop as upon failure the old_head will be updated, > > > another load is costly and not necessary. > > > > > > This helps a little on the latency,about 1~5%. > > > > > > Test result with the patch(two cores): > > > SP/SC bulk enq/dequeue (size: 8): 5.64 MP/MC bulk enq/dequeue (size: > > > 8): 9.58 SP/SC bulk enq/dequeue (size: 32): 1.98 MP/MC bulk > > > enq/dequeue (size: 32): 2.30 > > > > > > Fixes: 39368ebfc606 ("ring: introduce C11 memory model barrier > > > option") > > > Cc: stable@dpdk.org > > > > > > Signed-off-by: Gavin Hu > > > Reviewed-by: Honnappa Nagarahalli > > > Reviewed-by: Steve Capper > > > Reviewed-by: Ola Liljedahl > > > Reviewed-by: Jia He > > > Acked-by: Jerin Jacob > > > Tested-by: Jerin Jacob > > > --- > > > doc/guides/rel_notes/release_18_11.rst | 7 +++++++ > > > lib/librte_ring/rte_ring_c11_mem.h | 10 ++++------ > > > 2 files changed, 11 insertions(+), 6 deletions(-) > > > > > > diff --git a/doc/guides/rel_notes/release_18_11.rst > > > b/doc/guides/rel_notes/release_18_11.rst > > > index 376128f..b68afab 100644 > > > --- a/doc/guides/rel_notes/release_18_11.rst > > > +++ b/doc/guides/rel_notes/release_18_11.rst > > > @@ -69,6 +69,13 @@ New Features > > > checked out against that dma mask and rejected if out of range. If more > > than > > > one device has addressing limitations, the dma mask is the more > > restricted one. > > > > > > +* **Updated the ring library with C11 memory model.** > > > + > > > + Updated the ring library with C11 memory model, in our tests the > > > + changes decreased latency by 27~29% and 3~15% for MPMC and SPSC > > cases respectively. > > > + The real improvements may vary with the number of contending lcores > > > + and the size of ring. > > > + > > Is this a little misleading, and will users expect massive performance > > improvements generally? The C11 model seems to be used only on some, > > but not all, arm platforms, and then only with "make" builds. > > > > config/arm/meson.build: ['RTE_USE_C11_MEM_MODEL', false]] > > config/common_armv8a_linuxapp:CONFIG_RTE_USE_C11_MEM_MODEL=y > > config/common_base:CONFIG_RTE_USE_C11_MEM_MODEL=n > > config/defconfig_arm64-thunderx-linuxapp- > > gcc:CONFIG_RTE_USE_C11_MEM_MODEL=n > > > > /Bruce > > Thank you Bruce for the review, to limit the scope of improvement, I rewrite the note as follows, could you help review? Feel free to change anything if you like. > " Updated the ring library with C11 memory model, running ring_perf_autotest on Cavium ThunderX2 platform, the changes decreased latency by 27~29% and 3~15% for MPMC and SPSC cases (2 lcores) respectively. Note the changes help the relaxed memory ordering architectures (arm, ppc) only when CONFIG_RTE_USE_C11_MEM_MODEL=y was configured, no impact on strong memory ordering architectures like x86. To what extent they help the real use cases depends on other factors, like the number of contending readers/writers, size of the ring, whether or not it is on the critical path." I prefer your initial proposal which is more concise. What about something like this? * **Updated the C11 memory model version of ring library.** The latency is decreased for architectures using the C11 memory model version of the ring library. On Cavium ThunderX2 platform, the changes decreased latency by 27~29% and 3~15% for MPMC and SPSC cases respectively (with 2 lcores). The real improvements may vary with the number of contending lcores and the size of ring. About the patch itself: Acked-by: Olivier Matz Thanks