From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp.tuxdriver.com (charlotte.tuxdriver.com [70.61.120.58]) by dpdk.org (Postfix) with ESMTP id ADF3E2E81 for ; Thu, 18 Sep 2014 20:03:10 +0200 (CEST) Received: from hmsreliant.think-freely.org ([2001:470:8:a08:7aac:c0ff:fec2:933b] helo=localhost) by smtp.tuxdriver.com with esmtpsa (TLSv1:AES128-SHA:128) (Exim 4.63) (envelope-from ) id 1XUg8I-0003Ub-7F; Thu, 18 Sep 2014 14:08:54 -0400 Date: Thu, 18 Sep 2014 14:08:41 -0400 From: Neil Horman To: Thomas Monjalon Message-ID: <20140918180841.GN20389@hmsreliant.think-freely.org> References: <1410948102-12740-1-git-send-email-bruce.richardson@intel.com> <20140917152945.GF4213@localhost.localdomain> <59AF69C657FD0841A61C55336867B5B0343F355F@IRSMSX103.ger.corp.intel.com> <3289751.t83Qqk3rkH@xps13> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3289751.t83Qqk3rkH@xps13> User-Agent: Mutt/1.5.23 (2014-03-12) X-Spam-Score: -2.9 (--) X-Spam-Status: No Cc: dev@dpdk.org Subject: Re: [dpdk-dev] [PATCH 3/5] testpmd: Change rxfreet default to 32 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, 18 Sep 2014 18:03:10 -0000 On Thu, Sep 18, 2014 at 07:13:52PM +0200, Thomas Monjalon wrote: > 2014-09-18 15:53, Richardson, Bruce: > > > > --- a/app/test-pmd/testpmd.c > > > > +++ b/app/test-pmd/testpmd.c > > > > @@ -225,7 +225,7 @@ struct rte_eth_thresh tx_thresh = { > > > > /* > > > > * Configurable value of RX free threshold. > > > > */ > > > > -uint16_t rx_free_thresh = 0; /* Immediately free RX descriptors by default. */ > > > > +uint16_t rx_free_thresh = 32; /* Refill RX descriptors once every 32 packets > > > */ > > > > > > > > > > Why 32? Was that an experimentally determined value? > > > Does it hold true for all PMD's? > > > > This is primarily for the ixgbe PMD, which is right now the most > > highly tuned driver, but it works fine for all other ones too, > > as far as I'm aware. > > Yes, you are changing this value for all PMDs but you're targetting > only one. > These thresholds are dependent of the PMD implementation. There's > something wrong here. > I agree. Its fine to do this, but it does seem like the sample application should document why it does this and make note of the fact that other PMDs may have a separate optimal value. > > Basically, this is the minimum setting needed to enable either the > > bulk alloc or vector RX routines inside the ixgbe driver, so it's > > best made the default for that reason. Please see > > "check_rx_burst_bulk_alloc_preconditions()" in ixgbe_rxtx.c, and > > RX function assignment logic in "ixgbe_dev_rx_queue_setup()" in > > the same file. > > Since this parameter is so important, it could be a default value somewhere. > > I think we should split generic tuning parameters and tuning parameters > related to driver implementation or specific hardware. > Then we should provide some good default values for each of them. > At last, if needed, applications should be able to easily tune the > pmd-specific parameters. > I like this idea. I've not got an idea of how much work it is to do so, but in principle it makes sense. Perhaps for the immediate need, since rte_eth_rx_queue_setup allows the config struct to get passed directly to PMDs, we can create a reserved value RTE_ETH_RX_FREE_THRESH_OPTIMAL, that instructs the pmd to select whatever threshold is optimal for its own hardware? Neil > Thoughts? > > -- > Thomas >