On Thu, Oct 08, 2020 at 01:07:26PM +0000, Ananyev, Konstantin 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.po...@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;
> > +}
> > +
> > +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;
> > +}
> > +
> > 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,
>
> While I do understand the idea of having that value from consistency point of
> view,
> I wonder do we really need to allow user to specify values smaller then 128.
> At least on x86 we always have 128 bit SIMD enabled, even for
> -Dmachine=default.
> So seems no much point to forbid libraries using SSE code-path when compiler
> is free to insert SSE instructions on its own will.
>
The reason to support this is for testing purposes, as it allows an easy
way for a tester to check out any scalar code paths - which are often
common across architectures.
> > + RTE_MAX_128_SIMD = 128,
> > + RTE_MAX_256_SIMD = 256,
> > + RTE_MAX_512_SIMD = 512,
> > + RTE_MAX_SIMD_DISABLE = UINT16_MAX,
>
> As a nit, I think it is safe enough to have this last value
> (RTE_MAX_SIMD_DISABLE or RTE_MAX_SIMD_MAX) equal to (INT16_MAX + 1).
> That would be big enough to probably never hit actual HW limit,
> while it still remains power of two, as other values.
>
I actually think it's probably clearer as-is, because the fact of the rest
being powers of 2 is irrelevant since we just check greater than or less
than. If we did change it, then we need to put in a comment explaining why
the plus-one, while as it is now it's clearly a placeholder $BIGNUM.
/Bruce
