From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Zhang, Qi Z" Subject: Re: [PATCH] net/i40e: update tx_free_threshold to improve zero copy performance Date: Thu, 12 Apr 2018 12:20:07 +0000 Message-ID: <039ED4275CED7440929022BC67E7061153190506@SHSMSX103.ccr.corp.intel.com> References: <20180412053226.295226-1-junjie.j.chen@intel.com> <2601191342CEEE43887BDE71AB977258AE9143FC@IRSMSX102.ger.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Cc: "dev@dpdk.org" , "Chen, Junjie J" , "Chen@dpdk.org" To: "Ananyev, Konstantin" , "Chen, Junjie J" , "Xing, Beilei" Return-path: Received: from mga06.intel.com (mga06.intel.com [134.134.136.31]) by dpdk.org (Postfix) with ESMTP id 443761BD98 for ; Thu, 12 Apr 2018 14:20:12 +0200 (CEST) In-Reply-To: <2601191342CEEE43887BDE71AB977258AE9143FC@IRSMSX102.ger.corp.intel.com> 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" Hi Junjie: > -----Original Message----- > From: Ananyev, Konstantin > Sent: Thursday, April 12, 2018 7:52 PM > To: Chen, Junjie J ; Xing, Beilei > ; Zhang, Qi Z > Cc: dev@dpdk.org; Chen, Junjie J ; Chen@dpdk.org > Subject: RE: [dpdk-dev] [PATCH] net/i40e: update tx_free_threshold to > improve zero copy performance >=20 >=20 >=20 > > -----Original Message----- > > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Junjie Chen > > Sent: Thursday, April 12, 2018 6:32 AM > > To: Xing, Beilei ; Zhang, Qi Z > > > > Cc: dev@dpdk.org; Chen, Junjie J ; > > Chen@dpdk.org > > Subject: [dpdk-dev] [PATCH] net/i40e: update tx_free_threshold to > > improve zero copy performance > > > > From: "Chen, Junjie" > > > > When vhost backend works in dequeue zero copy mode, nic locks virtio's > > buffer until there is less or equal than tx_free_threshold buffer > > remain and then free number of tx burst buffer. This causes packets > > drop in virtio side and impacts zero copy performance. So we need to > > increase the tx_free_threshold to let nic free virtio's buffer as soon = as > possible. > > Also we keep the upper limit to tx max burst size to ensure least > > performance impact on non zero copy. >=20 > Ok but why vhost app can't just use tx_queue_setup() to specify desired v= alue > for tx_free_thresh? > Why instead we have to modify PMD to satisfy needs of one app? > Konstantin I think the commit log could include the explanation that this change is pr= oved not impact=20 driver's performance and it reduce total memory be locked by PMD Tx, so bas= ically it benefit application that share the same mem pool overall, vhost dequeue zero copy i= s one of the example. >=20 > > > > Signed-off-by: Chen, Junjie > > --- > > drivers/net/i40e/i40e_rxtx.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/drivers/net/i40e/i40e_rxtx.c > > b/drivers/net/i40e/i40e_rxtx.c index 56a854cec..d9569bdc9 100644 > > --- a/drivers/net/i40e/i40e_rxtx.c > > +++ b/drivers/net/i40e/i40e_rxtx.c > > @@ -2039,6 +2039,8 @@ i40e_dev_tx_queue_setup(struct rte_eth_dev > *dev, > > tx_conf->tx_rs_thresh : DEFAULT_TX_RS_THRESH); > > tx_free_thresh =3D (uint16_t)((tx_conf->tx_free_thresh) ? > > tx_conf->tx_free_thresh : DEFAULT_TX_FREE_THRESH); > > + if (tx_free_thresh < nb_desc - I40E_TX_MAX_BURST) > > + tx_free_thresh =3D nb_desc - I40E_TX_MAX_BURST; I think we'd better still allow application to set tx_free_thresh, since a = small tx_free_thresh may still have benefit to let driver handle the first = strike after device restarted So, nb_desc - I40E_TX_MAX_BURST can only be set when tx_conf->tx_rs_thresh = =3D 0 Regards Qi > > if (tx_rs_thresh >=3D (nb_desc - 2)) { > > PMD_INIT_LOG(ERR, "tx_rs_thresh must be less than the " > > "number of TX descriptors minus 2. " > > -- > > 2.16.0