On Thu, Apr 12, 2018 at 12:20:07PM +0000, Zhang, Qi Z wrote: > Hi Junjie: > > > -----Original Message----- > > From: Ananyev, Konstantin > > Sent: Thursday, April 12, 2018 7:52 PM > > To: Chen, Junjie J <junjie.j.c...@intel.com>; Xing, Beilei > > <beilei.x...@intel.com>; Zhang, Qi Z <qi.z.zh...@intel.com> > > Cc: dev@dpdk.org; Chen, Junjie J <junjie.j.c...@intel.com>; c...@dpdk.org > > Subject: RE: [dpdk-dev] [PATCH] net/i40e: update tx_free_threshold to > > improve zero copy performance > > > > > > > > > -----Original Message----- > > > From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Junjie Chen > > > Sent: Thursday, April 12, 2018 6:32 AM > > > To: Xing, Beilei <beilei.x...@intel.com>; Zhang, Qi Z > > > <qi.z.zh...@intel.com> > > > Cc: dev@dpdk.org; Chen, Junjie J <junjie.j.c...@intel.com>; > > > c...@dpdk.org > > > Subject: [dpdk-dev] [PATCH] net/i40e: update tx_free_threshold to > > > improve zero copy performance > > > > > > From: "Chen, Junjie" <junjie.j.c...@intel.com> > > > > > > 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 > > I think the commit log could include the explanation that this change is > proved not impact > driver's performance and it reduce total memory be locked by PMD Tx, so > basically it benefit > application that share the same mem pool overall, vhost dequeue zero copy is > one of the example. > > > > > > > > > Signed-off-by: Chen, Junjie <junjie.j.c...@intel.com> > > > --- > > > 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; > > 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 = 0 > > Regards > Qi > +1 for just changing in this case.
/Bruce
