> -----Original Message----- > From: dev [mailto:[email protected]] On Behalf Of Junjie Chen > Sent: Thursday, April 12, 2018 6:32 AM > To: Xing, Beilei <[email protected]>; Zhang, Qi Z <[email protected]> > Cc: [email protected]; Chen, Junjie J <[email protected]>; [email protected] > Subject: [dpdk-dev] [PATCH] net/i40e: update tx_free_threshold to improve > zero copy performance > > From: "Chen, Junjie" <[email protected]> > > 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.
Ok but why vhost app can't just use tx_queue_setup() to specify desired value for tx_free_thresh? Why instead we have to modify PMD to satisfy needs of one app? Konstantin > > Signed-off-by: Chen, Junjie <[email protected]> > --- > 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 = (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 = nb_desc - I40E_TX_MAX_BURST; > if (tx_rs_thresh >= (nb_desc - 2)) { > PMD_INIT_LOG(ERR, "tx_rs_thresh must be less than the " > "number of TX descriptors minus 2. " > -- > 2.16.0
