Re: [dpdk-dev] [PATCH v3] net/ice: add support for low Rx latency

["Zhang, Qi Z" <qi.z.zhang@intel.com>]

> -----Original Message-----
> From: Zhang, AlvinX <alvinx.zhang@intel.com>
> Sent: Friday, September 24, 2021 4:57 PM
> To: Zhang, Qi Z <qi.z.zhang@intel.com>
> Cc: dev@dpdk.org; Zhang, AlvinX <alvinx.zhang@intel.com>
> Subject: [PATCH v3] net/ice: add support for low Rx latency
> 
> This patch adds a devarg parameter to enable/disable low Rx latency.
> 
> Signed-off-by: Alvin Zhang <alvinx.zhang@intel.com>
> ---
> 
> v3: rebase to dpdk-next-net-intel
> ---
>  doc/guides/nics/ice.rst      | 12 ++++++++++++
>  drivers/net/ice/ice_ethdev.c | 26 +++++++++++++++++++++++---
> drivers/net/ice/ice_ethdev.h |  1 +
>  3 files changed, 36 insertions(+), 3 deletions(-)
> 
> diff --git a/doc/guides/nics/ice.rst b/doc/guides/nics/ice.rst index
> ebe2cbc..355f192 100644
> --- a/doc/guides/nics/ice.rst
> +++ b/doc/guides/nics/ice.rst
> @@ -227,6 +227,18 @@ Runtime Config Options
> 
>      -a af:00.0,pps_out='[pin:0]'
> 
> +- ``Low Rx latency`` (default ``0``)
> +
> +  vRAN workloads require low latency DPDK interface for the front haul
> + interface connection to Radio. By specifying ``1`` for parameter
> + ``rx-low-latency``, each completed Rx descriptor can be written
> + immediately  to host memory and the Rx interrupt latency can be reduced
> to 2us::
> +
> +    -a 0000:88:00.0,rx-low-latency=1
> +
> +  As a trade-off, this configuration may cause the packet processing
> + performance  degradation due to the PCI bandwidth limitation.
> +
>  Driver compilation and testing
>  ------------------------------
> 
> diff --git a/drivers/net/ice/ice_ethdev.c b/drivers/net/ice/ice_ethdev.c index
> e24a3b6..9edf811 100644
> --- a/drivers/net/ice/ice_ethdev.c
> +++ b/drivers/net/ice/ice_ethdev.c
> @@ -30,6 +30,7 @@
>  #define ICE_PROTO_XTR_ARG         "proto_xtr"
>  #define ICE_HW_DEBUG_MASK_ARG     "hw_debug_mask"
>  #define ICE_ONE_PPS_OUT_ARG       "pps_out"
> +#define ICE_RX_LOW_LATENCY        "rx-low-latency"

Should it has ARG suffix to align the naming rule?

> 
>  static const char * const ice_valid_args[] = {
>  	ICE_SAFE_MODE_SUPPORT_ARG,
> @@ -37,6 +38,7 @@
>  	ICE_PROTO_XTR_ARG,
>  	ICE_HW_DEBUG_MASK_ARG,
>  	ICE_ONE_PPS_OUT_ARG,
> +	ICE_RX_LOW_LATENCY,
>  	NULL
>  };
> 
> @@ -1956,6 +1958,9 @@ 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;
> @@ -3272,8 +3277,9 @@ 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) | @@ -3283,8
> +3289,21 @@ 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);
> +			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);
>  	}
> @@ -5497,7 +5516,8 @@ 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
> ea9d892..26f5c56 100644
> --- a/drivers/net/ice/ice_ethdev.h
> +++ b/drivers/net/ice/ice_ethdev.h
> @@ -476,6 +476,7 @@ 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;
> --
> 1.8.3.1