Re: [PATCH] common: introduce an integer log2 function

[Olivier MATZ <olivier.matz@6wind.com>]

I forgot to CC Alejandro for nfp.

Also CC Jerin: I think the same could be done in thunderx, but
I did not want to do the patch since it changes the base/ driver.


On Thu,  6 Apr 2017 16:15:36 +0200, Olivier Matz <olivier.matz@6wind.com> wrote:
> At some places, the log2() function is used despite this function
> works on float. This introduces a dependency to the math lib but
> most of the time it is not required because we want an integer log2.
> 
> Add a new helper to do this job and fix 2 drivers.
> 
> Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
> ---
>  drivers/net/nfp/nfp_net.c                  |  6 ++----
>  lib/librte_eal/common/include/rte_common.h | 17 +++++++++++++++++
>  mk/rte.app.mk                              |  2 +-
>  3 files changed, 20 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/nfp/nfp_net.c b/drivers/net/nfp/nfp_net.c
> index a1ad97ad5..0e6a729ef 100644
> --- a/drivers/net/nfp/nfp_net.c
> +++ b/drivers/net/nfp/nfp_net.c
> @@ -39,8 +39,6 @@
>   * Netronome vNIC DPDK Poll-Mode Driver: Main entry point
>   */
>  
> -#include <math.h>
> -
>  #include <rte_byteorder.h>
>  #include <rte_common.h>
>  #include <rte_log.h>
> @@ -1493,7 +1491,7 @@ nfp_net_rx_queue_setup(struct rte_eth_dev *dev,
>  	 * of descriptors in log2 format
>  	 */
>  	nn_cfg_writeq(hw, NFP_NET_CFG_RXR_ADDR(queue_idx), rxq->dma);
> -	nn_cfg_writeb(hw, NFP_NET_CFG_RXR_SZ(queue_idx), log2(nb_desc));
> +	nn_cfg_writeb(hw, NFP_NET_CFG_RXR_SZ(queue_idx), rte_log2_u32(nb_desc));
>  
>  	return 0;
>  }
> @@ -1647,7 +1645,7 @@ nfp_net_tx_queue_setup(struct rte_eth_dev *dev, uint16_t queue_idx,
>  	 * of descriptors in log2 format
>  	 */
>  	nn_cfg_writeq(hw, NFP_NET_CFG_TXR_ADDR(queue_idx), txq->dma);
> -	nn_cfg_writeb(hw, NFP_NET_CFG_TXR_SZ(queue_idx), log2(nb_desc));
> +	nn_cfg_writeb(hw, NFP_NET_CFG_TXR_SZ(queue_idx), rte_log2_u32(nb_desc));
>  
>  	return 0;
>  }
> diff --git a/lib/librte_eal/common/include/rte_common.h b/lib/librte_eal/common/include/rte_common.h
> index e057f6e21..eea0054c1 100644
> --- a/lib/librte_eal/common/include/rte_common.h
> +++ b/lib/librte_eal/common/include/rte_common.h
> @@ -326,6 +326,23 @@ rte_bsf32(uint32_t v)
>  	return __builtin_ctz(v);
>  }
>  
> +/**
> + * Return the rounded-up log2 of a integer.
> + *
> + * @param v
> + *     The input parameter.
> + * @return
> + *     The rounded-up log2 of the input, or 0 if the input is 0.
> + */
> +static inline uint32_t
> +rte_log2_u32(uint32_t v)
> +{
> +	if (v == 0)
> +		return 0;
> +	v = rte_align32pow2(v);
> +	return rte_bsf32(v);
> +}
> +
>  #ifndef offsetof
>  /** Return the offset of a field in a structure. */
>  #define offsetof(TYPE, MEMBER)  __builtin_offsetof (TYPE, MEMBER)
> diff --git a/mk/rte.app.mk b/mk/rte.app.mk
> index 4c659e971..2fcd388e6 100644
> --- a/mk/rte.app.mk
> +++ b/mk/rte.app.mk
> @@ -125,7 +125,7 @@ endif
>  _LDLIBS-$(CONFIG_RTE_LIBRTE_LIO_PMD)        += -lrte_pmd_lio
>  _LDLIBS-$(CONFIG_RTE_LIBRTE_MLX4_PMD)       += -lrte_pmd_mlx4 -libverbs
>  _LDLIBS-$(CONFIG_RTE_LIBRTE_MLX5_PMD)       += -lrte_pmd_mlx5 -libverbs
> -_LDLIBS-$(CONFIG_RTE_LIBRTE_NFP_PMD)        += -lrte_pmd_nfp -lm
> +_LDLIBS-$(CONFIG_RTE_LIBRTE_NFP_PMD)        += -lrte_pmd_nfp
>  _LDLIBS-$(CONFIG_RTE_LIBRTE_PMD_NULL)       += -lrte_pmd_null
>  _LDLIBS-$(CONFIG_RTE_LIBRTE_PMD_PCAP)       += -lrte_pmd_pcap -lpcap
>  _LDLIBS-$(CONFIG_RTE_LIBRTE_QEDE_PMD)       += -lrte_pmd_qede