> Rather than re-querying the HW each time a CPU flag is requested, we can
> just save the return value in the flags array. This should speed up
> repeated querying of CPU flags, and provides a workaround for a reported
> issue where errors are seen with constant querying of the AVX-512 CPU
> flag from a non-AVX VM.
>
> Bugzilla ID: 1501
>
> Signed-off-by: Bruce Richardson <bruce.richard...@intel.com>
>
> ---
> V2: Add compiler barrier to prevent issues with multi-threaded calls
> ---
> lib/eal/x86/rte_cpuflags.c | 22 +++++++++++++++++-----
> 1 file changed, 17 insertions(+), 5 deletions(-)
>
> diff --git a/lib/eal/x86/rte_cpuflags.c b/lib/eal/x86/rte_cpuflags.c
> index 26163ab746..90389c66fc 100644
> --- a/lib/eal/x86/rte_cpuflags.c
> +++ b/lib/eal/x86/rte_cpuflags.c
> @@ -8,8 +8,10 @@
> #include <errno.h>
> #include <stdint.h>
> #include <string.h>
> +#include <stdbool.h>
>
> #include "rte_cpuid.h"
> +#include "rte_atomic.h"
>
> /**
> * Struct to hold a processor feature entry
> @@ -21,12 +23,14 @@ struct feature_entry {
> uint32_t bit; /**< cpuid register bit */
> #define CPU_FLAG_NAME_MAX_LEN 64
> char name[CPU_FLAG_NAME_MAX_LEN]; /**< String for printing */
> + bool has_value;
> + bool value;
> };
>
> #define FEAT_DEF(name, leaf, subleaf, reg, bit) \
> [RTE_CPUFLAG_##name] = {leaf, subleaf, reg, bit, #name },
>
> -const struct feature_entry rte_cpu_feature_table[] = {
> +struct feature_entry rte_cpu_feature_table[] = {
> FEAT_DEF(SSE3, 0x00000001, 0, RTE_REG_ECX, 0)
> FEAT_DEF(PCLMULQDQ, 0x00000001, 0, RTE_REG_ECX, 1)
> FEAT_DEF(DTES64, 0x00000001, 0, RTE_REG_ECX, 2)
> @@ -147,7 +151,7 @@ const struct feature_entry rte_cpu_feature_table[] = {
> int
> rte_cpu_get_flag_enabled(enum rte_cpu_flag_t feature)
> {
> - const struct feature_entry *feat;
> + struct feature_entry *feat;
> cpuid_registers_t regs;
> unsigned int maxleaf;
>
> @@ -156,6 +160,8 @@ rte_cpu_get_flag_enabled(enum rte_cpu_flag_t feature)
> return -ENOENT;
>
> feat = &rte_cpu_feature_table[feature];
> + if (feat->has_value)
> + return feat->value;
>
> if (!feat->leaf)
> /* This entry in the table wasn't filled out! */
> @@ -163,8 +169,10 @@ rte_cpu_get_flag_enabled(enum rte_cpu_flag_t feature)
>
> maxleaf = __get_cpuid_max(feat->leaf & 0x80000000, NULL);
>
> - if (maxleaf < feat->leaf)
> - return 0;
> + if (maxleaf < feat->leaf) {
> + feat->value = 0;
> + goto out;
> + }
>
> #ifdef RTE_TOOLCHAIN_MSVC
> __cpuidex(regs, feat->leaf, feat->subleaf);
> @@ -175,7 +183,11 @@ rte_cpu_get_flag_enabled(enum rte_cpu_flag_t feature)
> #endif
>
> /* check if the feature is enabled */
> - return (regs[feat->reg] >> feat->bit) & 1;
> + feat->value = (regs[feat->reg] >> feat->bit) & 1;
> +out:
> + rte_compiler_barrier();
> + feat->has_value = true;
> + return feat->value;
> }
>
> const char *
> --
Acked-by: Konstantin Ananyev <konstantin.anan...@huawei.com>
> 2.43.0
>
