Re: [dpdk-dev] [PATCH v3 01/18] eal: add max SIMD bitwidth

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

Hi Ciara,

Please find some comments below.

On Wed, Sep 30, 2020 at 02:03:57PM +0100, Ciara Power wrote:
> This patch adds a max SIMD bitwidth EAL configuration. The API allows
> for an app to set this value. It can also be set using EAL argument
> --force-max-simd-bitwidth, which will lock the value and override any
> modifications made by the app.
> 
> Signed-off-by: Ciara Power <ciara.power@intel.com>
> 
> ---
> v3:
>   - Added enum value to essentially disable using max SIMD to choose
>     paths, intended for use by ARM SVE.
>   - Fixed parsing bitwidth argument to return an error for values
>     greater than uint16_t.
> v2: Added to Doxygen comment for API.
> ---
>  lib/librte_eal/common/eal_common_options.c | 64 ++++++++++++++++++++++
>  lib/librte_eal/common/eal_internal_cfg.h   |  8 +++
>  lib/librte_eal/common/eal_options.h        |  2 +
>  lib/librte_eal/include/rte_eal.h           | 33 +++++++++++
>  lib/librte_eal/rte_eal_version.map         |  4 ++
>  5 files changed, 111 insertions(+)
> 
> diff --git a/lib/librte_eal/common/eal_common_options.c b/lib/librte_eal/common/eal_common_options.c
> index a5426e1234..e9117a96af 100644
> --- a/lib/librte_eal/common/eal_common_options.c
> +++ b/lib/librte_eal/common/eal_common_options.c
> @@ -102,6 +102,7 @@ eal_long_options[] = {
>  	{OPT_MATCH_ALLOCATIONS, 0, NULL, OPT_MATCH_ALLOCATIONS_NUM},
>  	{OPT_TELEMETRY,         0, NULL, OPT_TELEMETRY_NUM        },
>  	{OPT_NO_TELEMETRY,      0, NULL, OPT_NO_TELEMETRY_NUM     },
> +	{OPT_FORCE_MAX_SIMD_BITWIDTH, 1, NULL, OPT_FORCE_MAX_SIMD_BITWIDTH_NUM},
>  	{0,                     0, NULL, 0                        }
>  };
>  
> @@ -1309,6 +1310,34 @@ eal_parse_iova_mode(const char *name)
>  	return 0;
>  }
>  
> +static int
> +eal_parse_simd_bitwidth(const char *arg, bool locked)
> +{
> +	char *end;
> +	unsigned long bitwidth;
> +	int ret;
> +	struct internal_config *internal_conf =
> +		eal_get_internal_configuration();
> +
> +	if (arg == NULL || arg[0] == '\0')
> +		return -1;
> +
> +	errno = 0;
> +	bitwidth = strtoul(arg, &end, 0);
> +
> +	/* check for errors */
> +	if (bitwidth > UINT16_MAX || errno != 0 || end == NULL || *end != '\0')
> +		return -1;
> +
> +	if (bitwidth == 0)
> +		bitwidth = UINT16_MAX;
> +	ret = rte_set_max_simd_bitwidth(bitwidth);
> +	if (ret < 0)
> +		return -1;
> +	internal_conf->max_simd_bitwidth.locked = locked;
> +	return 0;
> +}
> +
>  static int
>  eal_parse_base_virtaddr(const char *arg)
>  {
> @@ -1707,6 +1736,13 @@ eal_parse_common_option(int opt, const char *optarg,
>  	case OPT_NO_TELEMETRY_NUM:
>  		conf->no_telemetry = 1;
>  		break;
> +	case OPT_FORCE_MAX_SIMD_BITWIDTH_NUM:
> +		if (eal_parse_simd_bitwidth(optarg, 1) < 0) {
> +			RTE_LOG(ERR, EAL, "invalid parameter for --"
> +					OPT_FORCE_MAX_SIMD_BITWIDTH "\n");
> +			return -1;
> +		}
> +		break;
>  
>  	/* don't know what to do, leave this to caller */
>  	default:
> @@ -1903,6 +1939,33 @@ eal_check_common_options(struct internal_config *internal_cfg)
>  	return 0;
>  }
>  
> +uint16_t
> +rte_get_max_simd_bitwidth(void)
> +{
> +	const struct internal_config *internal_conf =
> +		eal_get_internal_configuration();
> +	return internal_conf->max_simd_bitwidth.bitwidth;
> +}

Should the return value be enum rte_max_simd_t?
If not, do we really need the enum definition?

> +
> +int
> +rte_set_max_simd_bitwidth(uint16_t bitwidth)
> +{
> +	struct internal_config *internal_conf =
> +		eal_get_internal_configuration();
> +	if (internal_conf->max_simd_bitwidth.locked) {
> +		RTE_LOG(NOTICE, EAL, "Cannot set max SIMD bitwidth - user runtime override enabled");
> +		return -EPERM;
> +	}
> +
> +	if (bitwidth != RTE_MAX_SIMD_DISABLE && (bitwidth < RTE_NO_SIMD ||
> +			!rte_is_power_of_2(bitwidth))) {
> +		RTE_LOG(ERR, EAL, "Invalid bitwidth value!\n");
> +		return -EINVAL;
> +	}
> +	internal_conf->max_simd_bitwidth.bitwidth = bitwidth;
> +	return 0;
> +}

Same question, should the parameter be enum rte_max_simd_t?

> +
>  void
>  eal_common_usage(void)
>  {
> @@ -1981,6 +2044,7 @@ eal_common_usage(void)
>  	       "  --"OPT_BASE_VIRTADDR"     Base virtual address\n"
>  	       "  --"OPT_TELEMETRY"   Enable telemetry support (on by default)\n"
>  	       "  --"OPT_NO_TELEMETRY"   Disable telemetry support\n"
> +	       "  --"OPT_FORCE_MAX_SIMD_BITWIDTH" Force the max SIMD bitwidth\n"
>  	       "\nEAL options for DEBUG use only:\n"
>  	       "  --"OPT_HUGE_UNLINK"       Unlink hugepage files after init\n"
>  	       "  --"OPT_NO_HUGE"           Use malloc instead of hugetlbfs\n"
> diff --git a/lib/librte_eal/common/eal_internal_cfg.h b/lib/librte_eal/common/eal_internal_cfg.h
> index 13f93388a7..367e0cc19e 100644
> --- a/lib/librte_eal/common/eal_internal_cfg.h
> +++ b/lib/librte_eal/common/eal_internal_cfg.h
> @@ -33,6 +33,12 @@ struct hugepage_info {
>  	int lock_descriptor;    /**< file descriptor for hugepage dir */
>  };
>  
> +struct simd_bitwidth {
> +	/**< flag indicating if bitwidth is locked from further modification */
> +	bool locked;
> +	uint16_t bitwidth; /**< bitwidth value */
> +};
> +
>  /**
>   * internal configuration
>   */
> @@ -85,6 +91,8 @@ struct internal_config {
>  	volatile unsigned int init_complete;
>  	/**< indicates whether EAL has completed initialization */
>  	unsigned int no_telemetry; /**< true to disable Telemetry */
> +	/** max simd bitwidth path to use */
> +	struct simd_bitwidth max_simd_bitwidth;
>  };
>  
>  void eal_reset_internal_config(struct internal_config *internal_cfg);
> diff --git a/lib/librte_eal/common/eal_options.h b/lib/librte_eal/common/eal_options.h
> index 89769d48b4..ef33979664 100644
> --- a/lib/librte_eal/common/eal_options.h
> +++ b/lib/librte_eal/common/eal_options.h
> @@ -85,6 +85,8 @@ enum {
>  	OPT_TELEMETRY_NUM,
>  #define OPT_NO_TELEMETRY      "no-telemetry"
>  	OPT_NO_TELEMETRY_NUM,
> +#define OPT_FORCE_MAX_SIMD_BITWIDTH  "force-max-simd-bitwidth"
> +	OPT_FORCE_MAX_SIMD_BITWIDTH_NUM,
>  	OPT_LONG_MAX_NUM
>  };
>  
> diff --git a/lib/librte_eal/include/rte_eal.h b/lib/librte_eal/include/rte_eal.h
> index ddcf6a2e7a..fb739f3474 100644
> --- a/lib/librte_eal/include/rte_eal.h
> +++ b/lib/librte_eal/include/rte_eal.h
> @@ -43,6 +43,14 @@ enum rte_proc_type_t {
>  	RTE_PROC_INVALID
>  };
>  
> +enum rte_max_simd_t {
> +	RTE_NO_SIMD = 64,
> +	RTE_MAX_128_SIMD = 128,
> +	RTE_MAX_256_SIMD = 256,
> +	RTE_MAX_512_SIMD = 512,
> +	RTE_MAX_SIMD_DISABLE = UINT16_MAX,
> +};

What is the difference between RTE_NO_SIMD and RTE_MAX_SIMD_DISABLE?

The default value in internal_config is 0, so in my understanding
rte_get_max_simd_bitwidth() will return 0 if --force-max-simd-bitwidth
is not passed. Is it expected?

Maybe I'm missing something, but I don't understand why the value in
internal_config is not set to the maximum supported SIMD bitwidth by
default, and optionally overriden by the command line argument, or by
the API.


> +
>  /**
>   * Get the process type in a multi-process setup
>   *
> @@ -51,6 +59,31 @@ enum rte_proc_type_t {
>   */
>  enum rte_proc_type_t rte_eal_process_type(void);
>  
> +/**
> + * Get the supported SIMD bitwidth.
> + *
> + * @return
> + *   uint16_t bitwidth.
> + */
> +__rte_experimental
> +uint16_t rte_get_max_simd_bitwidth(void);
> +
> +/**
> + * Set the supported SIMD bitwidth.
> + * This API should only be called once at initialization, before EAL init.
> + *
> + * @param bitwidth
> + *   uint16_t bitwidth.
> + * @return
> + *   0 on success.
> + * @return
> + *   -EINVAL on invalid bitwidth parameter.
> + * @return
> + *   -EPERM if bitwidth is locked.
> + */
> +__rte_experimental
> +int rte_set_max_simd_bitwidth(uint16_t bitwidth);
> +
>  /**
>   * Request iopl privilege for all RPL.
>   *
> diff --git a/lib/librte_eal/rte_eal_version.map b/lib/librte_eal/rte_eal_version.map
> index c32461c663..17a7195a3d 100644
> --- a/lib/librte_eal/rte_eal_version.map
> +++ b/lib/librte_eal/rte_eal_version.map
> @@ -397,6 +397,10 @@ EXPERIMENTAL {
>  	rte_service_lcore_may_be_active;
>  	rte_thread_register;
>  	rte_thread_unregister;
> +
> +	# added in 20.11
> +	rte_get_max_simd_bitwidth;
> +	rte_set_max_simd_bitwidth;
>  };
>  
>  INTERNAL {
> -- 
> 2.17.1
>