[ovs-dev,v6,4/6] dpdk: enable cpu feature detection.

This commit implements a method to retrieve the CPU ISA capabilities.
These ISA capabilities can be used in OVS to at runtime select a function
implementation to make the best use of the available ISA on the CPU.

Signed-off-by: Harry van Haaren <harry.van.haaren@intel.com>

---

v6:
- Add #if around RTE_CPUFLAG_AVX512F as it is not defined on CPU
  architectures that don't support the ISA. This check fixes compilation
  on those CPUs, as previously it had an undefined RTE_CPUFLAG_* error.
  (Reported by Travis, thanks Ian & William for running checks)

v5:
- Change API to return bool, and return to true/false (William Tu)
- Change error log to VLOG_ERR_ONCE instead of manual impl. (William Tu)

v4:
- Improve commit title and message
---
 lib/dpdk-stub.c |  9 +++++++++
 lib/dpdk.c      | 30 ++++++++++++++++++++++++++++++
 lib/dpdk.h      |  2 ++
 3 files changed, 41 insertions(+)

On 7/2/2020 6:42 PM, Harry van Haaren wrote:
> This commit implements a method to retrieve the CPU ISA capabilities.
> These ISA capabilities can be used in OVS to at runtime select a function
> implementation to make the best use of the available ISA on the CPU.
> 
> Signed-off-by: Harry van Haaren <harry.van.haaren@intel.com>
> 
LGTM, seems simple enough, I assume this gets called later in the series 
so in terms of testing will check it out there.

BR
Ian
> ---
> 
> v6:
> - Add #if around RTE_CPUFLAG_AVX512F as it is not defined on CPU
>    architectures that don't support the ISA. This check fixes compilation
>    on those CPUs, as previously it had an undefined RTE_CPUFLAG_* error.
>    (Reported by Travis, thanks Ian & William for running checks)
> 
> v5:
> - Change API to return bool, and return to true/false (William Tu)
> - Change error log to VLOG_ERR_ONCE instead of manual impl. (William Tu)
> 
> v4:
> - Improve commit title and message
> ---
>   lib/dpdk-stub.c |  9 +++++++++
>   lib/dpdk.c      | 30 ++++++++++++++++++++++++++++++
>   lib/dpdk.h      |  2 ++
>   3 files changed, 41 insertions(+)
> 
> diff --git a/lib/dpdk-stub.c b/lib/dpdk-stub.c
> index c332c217c..b7d577870 100644
> --- a/lib/dpdk-stub.c
> +++ b/lib/dpdk-stub.c
> @@ -79,6 +79,15 @@ print_dpdk_version(void)
>   {
>   }
>   
> +bool
> +dpdk_get_cpu_has_isa(const char *arch OVS_UNUSED,
> +                     const char *feature OVS_UNUSED)
> +{
> +    VLOG_ERR_ONCE("DPDK not supported in this version of Open vSwitch, "
> +                  "cannot use CPU flag based optimizations");
> +    return false;
> +}
> +
>   void
>   dpdk_status(const struct ovsrec_open_vswitch *cfg)
>   {
> diff --git a/lib/dpdk.c b/lib/dpdk.c
> index 31450d470..64a0d43e8 100644
> --- a/lib/dpdk.c
> +++ b/lib/dpdk.c
> @@ -22,6 +22,7 @@
>   #include <sys/stat.h>
>   #include <getopt.h>
>   
> +#include <rte_cpuflags.h>
>   #include <rte_errno.h>
>   #include <rte_log.h>
>   #include <rte_memzone.h>
> @@ -513,6 +514,35 @@ print_dpdk_version(void)
>       puts(rte_version());
>   }
>   
> +#define CHECK_CPU_FEATURE(feature, name_str, RTE_CPUFLAG)               \
> +    do {                                                                \
> +        if (strncmp(feature, name_str, strlen(name_str)) == 0) {        \
> +            int has_isa = rte_cpu_get_flag_enabled(RTE_CPUFLAG);        \
> +            VLOG_DBG("CPU flag %s, available %s\n", name_str,           \
> +                      has_isa ? "yes" : "no");                          \
> +            return true;                                                \
> +        }                                                               \
> +    } while (0)
> +
> +bool
> +dpdk_get_cpu_has_isa(const char *arch, const char *feature)
> +{
> +    /* Ensure Arch is x86_64 */
> +    if (strncmp(arch, "x86_64", 6) != 0) {
> +        return false;
> +    }
> +
> +#if __x86_64__
> +    /* CPU flags only defined for the architecture that support it */
> +    CHECK_CPU_FEATURE(feature, "avx512f", RTE_CPUFLAG_AVX512F);
> +    CHECK_CPU_FEATURE(feature, "bmi2", RTE_CPUFLAG_BMI2);
> +#endif
> +
> +    VLOG_WARN("Unknown CPU arch,feature: %s,%s. Returning not supported.\n",
> +              arch, feature);
> +    return false;
> +}
> +
>   void
>   dpdk_status(const struct ovsrec_open_vswitch *cfg)
>   {
> diff --git a/lib/dpdk.h b/lib/dpdk.h
> index 736a64279..445a51d06 100644
> --- a/lib/dpdk.h
> +++ b/lib/dpdk.h
> @@ -44,4 +44,6 @@ bool dpdk_per_port_memory(void);
>   bool dpdk_available(void);
>   void print_dpdk_version(void);
>   void dpdk_status(const struct ovsrec_open_vswitch *);
> +bool dpdk_get_cpu_has_isa(const char *arch, const char *feature);
> +
>   #endif /* dpdk.h */
>