From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga14.intel.com (mga14.intel.com [192.55.52.115]) by dpdk.org (Postfix) with ESMTP id 5A9176CBA for ; Thu, 19 May 2016 10:50:53 +0200 (CEST) Received: from orsmga001.jf.intel.com ([10.7.209.18]) by fmsmga103.fm.intel.com with ESMTP; 19 May 2016 01:50:52 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.26,333,1459839600"; d="scan'208";a="957905492" Received: from bricha3-mobl3.ger.corp.intel.com ([10.237.221.57]) by orsmga001.jf.intel.com with SMTP; 19 May 2016 01:50:48 -0700 Received: by (sSMTP sendmail emulation); Thu, 19 May 2016 09:50:48 +0025 Date: Thu, 19 May 2016 09:50:48 +0100 From: Bruce Richardson To: Jerin Jacob Cc: dev@dpdk.org, thomas.monjalon@6wind.com, konstantin.ananyev@intel.com, viktorin@rehivetech.com, jianbo.liu@linaro.org Message-ID: <20160519085047.GA17500@bricha3-MOBL3> References: <1463579863-32053-1-git-send-email-jerin.jacob@caviumnetworks.com> <20160518164300.GA12324@bricha3-MOBL3> <20160518185011.GA4432@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160518185011.GA4432@localhost.localdomain> Organization: Intel Shannon Ltd. User-Agent: Mutt/1.5.23 (2014-03-12) Subject: Re: [dpdk-dev] [PATCH] mbuf: make rearm_data address naturally aligned 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: Thu, 19 May 2016 08:50:53 -0000 On Thu, May 19, 2016 at 12:20:16AM +0530, Jerin Jacob wrote: > On Wed, May 18, 2016 at 05:43:00PM +0100, Bruce Richardson wrote: > > On Wed, May 18, 2016 at 07:27:43PM +0530, Jerin Jacob wrote: > > > To avoid multiple stores on fast path, Ethernet drivers > > > aggregate the writes to data_off, refcnt, nb_segs and port > > > to an uint64_t data and write the data in one shot > > > with uint64_t* at &mbuf->rearm_data address. > > > > > > Some of the non-IA platforms have store operation overhead > > > if the store address is not naturally aligned.This patch > > > fixes the performance issue on those targets. > > > > > > Signed-off-by: Jerin Jacob > > > --- > > > > > > Tested this patch on IA and non-IA(ThunderX) platforms. > > > This patch shows 400Kpps/core improvement on ThunderX + ixgbe + vector environment. > > > and this patch does not have any overhead on IA platform. > > > > > > Have tried an another similar approach by replacing "buf_len" with "pad" > > > (in this patch context), > > > Since it has additional overhead on read and then mask to keep "buf_len" intact, > > > not much improvement is not shown. > > > ref: http://dpdk.org/ml/archives/dev/2016-May/038914.html > > > > > > --- > > While this will work and from your tests doesn't seem to have a performance > > impact, I'm not sure I particularly like it. It's extending out the end of > > cacheline0 of the mbuf by 16 bytes, though I suppose it's not technically using > > up any more space of it. > > Extending by 2 bytes. Right ?. Yes, I guess, Now we using only 56 out of 64 bytes > in the first 64-byte cache line. > > > > > What I'm wondering about though, is do we have any usecases where we need a > > variable buf_len for packets for RX. These mbufs come directly from a mempool, > > which is generally understood to be a set of fixed-sized buffers. I realise that > > this change was made in the past after some discussion, but one of the key points > > there [at least to my reading] was that - even though nobody actually made a > > concrete case where they had variable-sized buffers - having support for them > > made no performance difference. > > > > The latter part of that has now changed, and supporting variable-sized mbufs > > from an mbuf pool has a perf impact. Do we definitely need that functionality, > > because the easiest fix here is just to move the rxrearm marker back above > > mbuf_len as it was originally in releases like 1.8? > > And initialize the buf_len with mp->elt_size - sizeof(struct rte_mbuf). > Right? > > I don't have a strong opinion on this, I can do this if there is no > objection on this. Let me know. > > However, I do see in future, "buf_len" may belong at the end of the first 64 byte > cache line as currently "port" is defined as uint8_t, IMO, that is less. > We may need to increase that uint16_t. The reason why I think that > because, Currently in ThunderX HW, we do have 128VFs per socket for > built-in NIC, So, the two node configuration and one external PCIe NW card > configuration can easily go beyond 256 ports. > Ok, good point. If you think it's needed, and if we are changing the mbuf structure, it might be a good time to extend that field while you are at it, save a second ABI break later on. /Bruce > > > > Regards, > > /Bruce > > > > Ref: http://dpdk.org/ml/archives/dev/2014-December/009432.html > >