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

[Bruce Richardson]

On Thu, Oct 08, 2020 at 03:07:54PM +0100, Ananyev, Konstantin wrote:
> 
> > 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.power at 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.
> 
> If it is just for testing things in a consistent way, then it is  probably ok.
> The thing that worries me - later in this series there are patches
> that insert extra checks into inline functions that use SSE instincts:
> https://patches.dpdk.org/patch/79355/ (lpm: choose vector path at runtime).
> Which seems like a total overkill for me.
> 
> >
> > > > +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.
> 
> Well, rte_set_max_simd_bitwidth() does accept only power of two values
> _AND_ this special one (UINT16_MAX).
> By changing it to 2^15, we can remove that special value test.
> 
> > If we did change it, then we need to put in a comment explaining why
> > the plus-one,
> 
> I don't think it is that big deal to put a comment,
> plus for UINT16_MAX we do need some explanation too, right?
> 
I'm ok either way. Ciara, what do you think?