> -----Original Message-----
> From: Kevin Traynor <ktray...@redhat.com>
> Sent: Saturday, September 18, 2021 1:25 AM
> To: Zhang, AlvinX <alvinx.zh...@intel.com>; Zhang, Qi Z
> <qi.z.zh...@intel.com>; Guo, Junfeng <junfeng....@intel.com>
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH] net/ice: add ability to reduce the Rx latency
>
> On 14/09/2021 02:31, Alvin Zhang wrote:
> > This patch adds a devarg parameter to enable/disable reducing the Rx
> > latency.
> >
> > Signed-off-by: Alvin Zhang <alvinx.zh...@intel.com>
> > ---
> > doc/guides/nics/ice.rst | 8 ++++++++
> > drivers/net/ice/ice_ethdev.c | 26 +++++++++++++++++++++++---
> > drivers/net/ice/ice_ethdev.h | 1 +
> > 3 files changed, 32 insertions(+), 3 deletions(-)
> >
> > diff --git a/doc/guides/nics/ice.rst b/doc/guides/nics/ice.rst index
> > 5bc472f..3db0430 100644
> > --- a/doc/guides/nics/ice.rst
> > +++ b/doc/guides/nics/ice.rst
> > @@ -219,6 +219,14 @@ Runtime Config Options
> >
> > These ICE_DBG_XXX are defined in ``drivers/net/ice/base/ice_type.h``.
> >
> > +- ``Reduce Rx interrupts and latency`` (default ``0``)
> > +
> > + vRAN workloads require low latency DPDK interface for the front
> > + haul interface connection to Radio. Now we can reduce Rx interrupts
> > + and latency by specify ``1`` for parameter ``rx-low-latency``::
> > +
> > + -a 0000:88:00.0,rx-low-latency=1
> > +
>
> When would a user select this and when not? What is the trade off?
>
> The text is a bit unclear. It looks below like it reduces the interrupt
> latency, but
> not the number of interrupts. Maybe I got it wrong.
Yes, it reduces the interrupt latency,
We will refine the doc in next patch.
>
>
> > Driver compilation and testing
> > ------------------------------
> >
> > diff --git a/drivers/net/ice/ice_ethdev.c
> > b/drivers/net/ice/ice_ethdev.c index a4cd39c..85662e4 100644
> > --- a/drivers/net/ice/ice_ethdev.c
> > +++ b/drivers/net/ice/ice_ethdev.c
> > @@ -29,12 +29,14 @@
> > #define ICE_PIPELINE_MODE_SUPPORT_ARG "pipeline-mode-support"
> > #define ICE_PROTO_XTR_ARG "proto_xtr"
> > #define ICE_HW_DEBUG_MASK_ARG "hw_debug_mask"
> > +#define ICE_RX_LOW_LATENCY "rx-low-latency"
> >
> > static const char * const ice_valid_args[] = {
> > ICE_SAFE_MODE_SUPPORT_ARG,
> > ICE_PIPELINE_MODE_SUPPORT_ARG,
> > ICE_PROTO_XTR_ARG,
> > ICE_HW_DEBUG_MASK_ARG,
> > + ICE_RX_LOW_LATENCY,
> > NULL
> > };
> >
> > @@ -1827,6 +1829,9 @@ static int ice_parse_devargs(struct rte_eth_dev
> *dev)
> > if (ret)
> > goto bail;
> >
> > + ret = rte_kvargs_process(kvlist, ICE_RX_LOW_LATENCY,
> > + &parse_bool, &ad->devargs.rx_low_latency);
> > +
> > bail:
> > rte_kvargs_free(kvlist);
> > return ret;
> > @@ -3144,8 +3149,9 @@ static int ice_init_rss(struct ice_pf *pf) {
> > struct ice_hw *hw = ICE_VSI_TO_HW(vsi);
> > uint32_t val, val_tx;
> > - int i;
> > + int rx_low_latency, i;
> >
> > + rx_low_latency = vsi->adapter->devargs.rx_low_latency;
> > for (i = 0; i < nb_queue; i++) {
> > /*do actual bind*/
> > val = (msix_vect & QINT_RQCTL_MSIX_INDX_M) | @@ -3155,8
> +3161,21 @@
> > static int ice_init_rss(struct ice_pf *pf)
> >
> > PMD_DRV_LOG(INFO, "queue %d is binding to vect %d",
> > base_queue + i, msix_vect);
> > +
> > /* set ITR0 value */
> > - ICE_WRITE_REG(hw, GLINT_ITR(0, msix_vect), 0x2);
> > + if (rx_low_latency) {
> > + /**
> > + * Empirical configuration for optimal real time
> > + * latency reduced interrupt throttling to 2us
> > + */
> > + ICE_WRITE_REG(hw, GLINT_ITR(0, msix_vect), 0x1);
>
> Why not set this to 0? "Setting the INTERVAL to zero enables immediate
> interrupt."
>
> > + ICE_WRITE_REG(hw, QRX_ITR(base_queue + i),
> > + QRX_ITR_NO_EXPR_M);
> > + } else {
> > + ICE_WRITE_REG(hw, GLINT_ITR(0, msix_vect), 0x2);
> > + ICE_WRITE_REG(hw, QRX_ITR(base_queue + i), 0);
> > + }
> > +
> > ICE_WRITE_REG(hw, QINT_RQCTL(base_queue + i), val);
> > ICE_WRITE_REG(hw, QINT_TQCTL(base_queue + i), val_tx);
> > }
> > @@ -5314,7 +5333,8 @@ static int ice_xstats_get_names(__rte_unused
> struct rte_eth_dev *dev,
> > ICE_HW_DEBUG_MASK_ARG "=0xXXX"
> > ICE_PROTO_XTR_ARG
> "=[queue:]<vlan|ipv4|ipv6|ipv6_flow|tcp|ip_offset>"
> > ICE_SAFE_MODE_SUPPORT_ARG "=<0|1>"
> > - ICE_PIPELINE_MODE_SUPPORT_ARG "=<0|1>");
> > + ICE_PIPELINE_MODE_SUPPORT_ARG "=<0|1>"
> > + ICE_RX_LOW_LATENCY "=<0|1>");
> >
> > RTE_LOG_REGISTER_SUFFIX(ice_logtype_init, init, NOTICE);
> > RTE_LOG_REGISTER_SUFFIX(ice_logtype_driver, driver, NOTICE); diff
> > --git a/drivers/net/ice/ice_ethdev.h b/drivers/net/ice/ice_ethdev.h
> > index b4bf651..c61cc1f 100644
> > --- a/drivers/net/ice/ice_ethdev.h
> > +++ b/drivers/net/ice/ice_ethdev.h
> > @@ -463,6 +463,7 @@ struct ice_pf {
> > * Cache devargs parse result.
> > */
> > struct ice_devargs {
> > + int rx_low_latency;
> > int safe_mode_support;
> > uint8_t proto_xtr_dflt;
> > int pipe_mode_support;
> >
