[v2,17/17] net: add checks for max SIMD bitwidth

  When choosing a vector path to take, an extra condition must be
satisfied to ensure the max SIMD bitwidth allows for the CPU enabled
path. This check is done just before the handler is called, it cannot
be done when setting the handlers initially as the EAL max simd bitwidth
value has not yet been set.

Cc: Jasvinder Singh <jasvinder.singh@intel.com>

Signed-off-by: Ciara Power <ciara.power@intel.com>
---
 lib/librte_net/rte_net_crc.c | 8 ++++++++
 1 file changed, 8 insertions(+)
  

> -----Original Message-----
> From: Power, Ciara <ciara.power@intel.com>
> Sent: Thursday, August 27, 2020 5:13 PM
> To: dev@dpdk.org
> Cc: Power, Ciara <ciara.power@intel.com>; Singh, Jasvinder
> <jasvinder.singh@intel.com>; Olivier Matz <olivier.matz@6wind.com>
> Subject: [PATCH v2 17/17] net: add checks for max SIMD bitwidth
> 
> When choosing a vector path to take, an extra condition must be satisfied to
> ensure the max SIMD bitwidth allows for the CPU enabled path. This check is
> done just before the handler is called, it cannot be done when setting the
> handlers initially as the EAL max simd bitwidth value has not yet been set.
> 
> Cc: Jasvinder Singh <jasvinder.singh@intel.com>
> 
> Signed-off-by: Ciara Power <ciara.power@intel.com>
> ---
>  lib/librte_net/rte_net_crc.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/lib/librte_net/rte_net_crc.c b/lib/librte_net/rte_net_crc.c index
> 9fd4794a9d..d3d3206919 100644
> --- a/lib/librte_net/rte_net_crc.c
> +++ b/lib/librte_net/rte_net_crc.c
> @@ -9,6 +9,7 @@
>  #include <rte_cpuflags.h>
>  #include <rte_common.h>
>  #include <rte_net_crc.h>
> +#include <rte_eal.h>
> 
>  #if defined(RTE_ARCH_X86_64) &&
> defined(RTE_MACHINE_CPUFLAG_PCLMULQDQ)
>  #define X86_64_SSE42_PCLMULQDQ     1
> @@ -60,6 +61,8 @@ static rte_net_crc_handler handlers_neon[] = {  };
> #endif
> 
> +static uint16_t max_simd_bitwidth;
> +
>  /**
>   * Reflect the bits about the middle
>   *
> @@ -175,6 +178,11 @@ rte_net_crc_calc(const void *data,
>  	uint32_t ret;
>  	rte_net_crc_handler f_handle;
> 
> +	if (max_simd_bitwidth == 0)
> +		max_simd_bitwidth = rte_get_max_simd_bitwidth();
> +	if (max_simd_bitwidth < RTE_MAX_128_SIMD &&
> +			handlers != handlers_scalar)
> +		rte_net_crc_set_alg(RTE_NET_CRC_SCALAR);


Above change doesn't seem right as rte_net_crc_set_alg () is invoked everytime when crc is computed. It potentially adds branches in runtime.  In my opinion,  bit width should be checked inside rte_net_crc_set_alg () function which is supposed to be used during initialization stage after eal sets the max simd bit width. 

>  	f_handle = handlers[type];
>  	ret = f_handle(data, data_len);
> 
> --
> 2.17.1