From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f54.google.com (mail-wm0-f54.google.com [74.125.82.54]) by dpdk.org (Postfix) with ESMTP id 88FE65AB2 for ; Wed, 9 Mar 2016 17:22:46 +0100 (CET) Received: by mail-wm0-f54.google.com with SMTP id p65so78327500wmp.0 for ; Wed, 09 Mar 2016 08:22:46 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=6wind-com.20150623.gappssmtp.com; s=20150623; h=from:to:cc:subject:date:message-id:organization:user-agent :in-reply-to:references:mime-version:content-transfer-encoding; bh=evC5C0aZxyHAFLnP+Q7/tN2PhGJ5wKnXhX7/9uHhJHU=; b=vYTuX7CL/qU7FzaKngQ0gem1JvVHq4jYddzUm34xdKkJLZ0+R3khnhpKMQrTEphrh9 byAMt7fv+zzmDMHOjHNMHUeKzXP87pRby3mFgYxEmotVqVA8/et6EvVC9h47YmTxneuS b0fBXrGvqnS9Np8G2XXOgFizFGjKKaVjreIVVz15dAES4lGcjGpH8RczSC25KRABMrxH SmlXHWGcn/KS6IPQqGsdZ46MGmW53BlxC/5OExdH7azCXuSCyh97rGXXsLvp1icjXdHr ykXRH2LyNTfeZiOKfuI5R1vjrklmPvu7tSZeFzBM4vGX3QvO7JOThSFEaEkS8hsgdTPX NchQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:cc:subject:date:message-id:organization :user-agent:in-reply-to:references:mime-version :content-transfer-encoding; bh=evC5C0aZxyHAFLnP+Q7/tN2PhGJ5wKnXhX7/9uHhJHU=; b=DRuDKBD8sLDAHhB9U2vnm7M0GpEwaeFoSLTyvzekx2tpCMvTkCp7XbafhrP8k4nFn7 OW+Au2ilx+g3dbTrjAqVX4N6rvc55N9zOISOZIRURor1rq5UxqsK3VdlKqa+9hO57LOS TVXyIdJR7mZWBTQ+ZTGasbPWZ1JKlrVC7BheltxZl6hhpm7DT7EZ5Q6XRcDX0wd5YIA4 kzX4kR8UZ3Q9ZMqqQcvhAZACaPbf9RtjC2oHer0w6gyKZQO7zpNdQAc9GpxR0+aw17pd YDRa/DcM8UqVUWgPQCZiWTcOz70hiRkys6xGuc+ptvDA15Li/s8YF/+4oIOg8f0gdeQ/ UHlQ== X-Gm-Message-State: AD7BkJLiuummNLmOifokhEJ7LAJW+a0mKbdOafdRA+yGsJovidmOxwqbEcbh2xdeZw4j8iGf X-Received: by 10.28.171.8 with SMTP id u8mr25574473wme.97.1457540566304; Wed, 09 Mar 2016 08:22:46 -0800 (PST) Received: from xps13.localnet (91.111.75.86.rev.sfr.net. [86.75.111.91]) by smtp.gmail.com with ESMTPSA id k125sm24338277wmb.14.2016.03.09.08.22.45 (version=TLSv1/SSLv3 cipher=OTHER); Wed, 09 Mar 2016 08:22:45 -0800 (PST) From: Thomas Monjalon To: "Ananyev, Konstantin" Date: Wed, 09 Mar 2016 17:21:06 +0100 Message-ID: <2591002.JUd3oniQam@xps13> Organization: 6WIND User-Agent: KMail/4.14.10 (Linux/4.1.6-1-ARCH; KDE/4.14.11; x86_64; ; ) In-Reply-To: <2601191342CEEE43887BDE71AB97725836B1A6C4@irsmsx105.ger.corp.intel.com> References: <1452869038-9140-1-git-send-email-tomaszx.kulasek@intel.com> <2507362.eR3Lu18VyN@xps13> <2601191342CEEE43887BDE71AB97725836B1A6C4@irsmsx105.ger.corp.intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Cc: dev@dpdk.org Subject: Re: [dpdk-dev] [PATCH v2 1/2] ethdev: add buffered tx api 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: Wed, 09 Mar 2016 16:22:46 -0000 2016-03-09 16:17, Ananyev, Konstantin: > From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com] > > 2016-03-09 15:42, Ananyev, Konstantin: > > > From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com] > > > > 2016-03-09 15:23, Ananyev, Konstantin: > > > > > > > > > > > > 2016-03-09 13:36, Ananyev, Konstantin: > > > > > > > > > + if (to_send == 0) > > > > > > > > > + return 0; > > > > > > > > > > > > > > > > Why this check is done in the lib? > > > > > > > > What is the performance gain if we are idle? > > > > > > > > It can be done outside if needed. > > > > > > > > > > > > > > Yes, that could be done outside, but if user has to do it anyway, > > > > > > > why not to put it inside? > > > > > > > I don't expect any performance gain/loss because of that - > > > > > > > just seems a bit more convenient to the user. > > > > > > > > > > > > It is handling an idle case so there is no gain obviously. > > > > > > But the condition branching is surely a loss. > > > > > > > > > > I suppose that condition should always be checked: > > > > > either in user code prior to function call or inside the > > > > > function call itself. > > > > > So don't expect any difference in performance here... > > > > > Do you have any particular example when you think it would? > > > > > Or are you talking about rte_eth_tx_buffer() calling > > > > > rte_eth_tx_buffer_flush() internally? > > > > > For that one - both are flush is 'static inline' , so I expect > > > > > compiler be smart enough to remove this redundant check. > > > > > > > > > > > So why the user would you like to do this check? > > > > > Just for user convenience - to save him doing that manually. > > > > > > > > Probably I've missed something. If we remove this check, the function > > > > will do nothing, right? How is it changing the behaviour? > > > > > > If we'll remove that check, then > > > rte_eth_tx_burst(...,nb_pkts=0)->(*dev->tx_pkt_burst)(...,nb_pkts=0) > > > will be called. > > > So in that case it might be even slower, as we'll have to do a proper call. > > > > If there is no packet, we have time to do a useless call. > > One lcore can do TX for several queues/ports. > Let say we have N queues to handle, but right now traffic is going only through > one of them. > That means we'll have to do N-1 useless calls and reduce number of cycles > available to send actual traffic. OK, good justification, thanks. > > > Of course user can avoid it by: > > > > > > If(tx_buffer->nb_pkts != 0) > > > rte_eth_tx_buffer_flush(port, queue, tx_buffer); > > > > > > But as I said what for to force user to do that? > > > Why not to make this check inside the function? > > > > Because it may be slower when there are some packets > > and will "accelerate" only the no-packet case. > > > > We do not progress in this discussion. > > It is not a big deal, > > Exactly. > > >just a non sense. > > Look at what most of current DPDK examples do: they do check manually > does nb_pkts==0 or not, if not call tx_burst(). > For me it makes sense to move that check into the library function - > so each and every caller doesn't have to do it manually. > > > So I agree to keep it if we change the website to announce that DPDK > > accelerates the idle processing ;) > > That's fine by me, but at first I suppose you'll have to provide some data > showing that this approach slowdowns things, right? :) You got me