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From: "Ananyev, Konstantin" <konstantin.ananyev@intel.com>
To: "Richardson, Bruce" <bruce.richardson@intel.com>
CC: "Power, Ciara" <ciara.power@intel.com>, "dev@dpdk.org" <dev@dpdk.org>,
"Ray Kinsella" <mdr@ashroe.eu>, Neil Horman <nhorman@tuxdriver.com>
Thread-Topic: [dpdk-dev] [PATCH v3 01/18] eal: add max SIMD bitwidth
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Subject: Re: [dpdk-dev] [PATCH v3 01/18] eal: add max SIMD bitwidth
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> 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@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[] =3D {
> > > {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 =3D
> > > + eal_get_internal_configuration();
> > > +
> > > + if (arg =3D=3D NULL || arg[0] =3D=3D '\0')
> > > + return -1;
> > > +
> > > + errno =3D 0;
> > > + bitwidth =3D strtoul(arg, &end, 0);
> > > +
> > > + /* check for errors */
> > > + if (bitwidth > UINT16_MAX || errno !=3D 0 || end =3D=3D NULL || *en=
d !=3D '\0')
> > > + return -1;
> > > +
> > > + if (bitwidth =3D=3D 0)
> > > + bitwidth =3D UINT16_MAX;
> > > + ret =3D rte_set_max_simd_bitwidth(bitwidth);
> > > + if (ret < 0)
> > > + return -1;
> > > + internal_conf->max_simd_bitwidth.locked =3D locked;
> > > + return 0;
> > > +}
> > > +
> > > static int
> > > eal_parse_base_virtaddr(const char *arg)
> > > {
> > > @@ -1707,6 +1736,13 @@ eal_parse_common_option(int opt, const char *o=
ptarg,
> > > case OPT_NO_TELEMETRY_NUM:
> > > conf->no_telemetry =3D 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_confi=
g *internal_cfg)
> > > return 0;
> > > }
> > >
> > > +uint16_t
> > > +rte_get_max_simd_bitwidth(void)
> > > +{
> > > + const struct internal_config *internal_conf =3D
> > > + 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 =3D
> > > + 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 !=3D 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 =3D 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 defau=
lt)\n"
> > > " --"OPT_NO_TELEMETRY" Disable telemetry support\n"
> > > + " --"OPT_FORCE_MAX_SIMD_BITWIDTH" Force the max SIMD bitwid=
th\n"
> > > "\nEAL options for DEBUG use only:\n"
> > > " --"OPT_HUGE_UNLINK" Unlink hugepage files after ini=
t\n"
> > > " --"OPT_NO_HUGE" Use malloc instead of hugetlbfs=
\n"
> > > diff --git a/lib/librte_eal/common/eal_internal_cfg.h b/lib/librte_ea=
l/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 modificatio=
n */
> > > + 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/com=
mon/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/includ=
e/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 =3D 64,
> >
> > While I do understand the idea of having that value from consistency po=
int 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=
=3Ddefault.
> > So seems no much point to forbid libraries using SSE code-path when com=
piler
> > is free to insert SSE instructions on its own will.
> >
>=20
> 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.
>=20
> > > + RTE_MAX_128_SIMD =3D 128,
> > > + RTE_MAX_256_SIMD =3D 256,
> > > + RTE_MAX_512_SIMD =3D 512,
> > > + RTE_MAX_SIMD_DISABLE =3D 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.
> >
>=20
> I actually think it's probably clearer as-is, because the fact of the res=
t
> being powers of 2 is irrelevant since we just check greater than or less
> than.=20
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. =20
> If we did change it, then we need to put in a comment explaining why
> the plus-one,=20
I don't think it is that big deal to put a comment,
plus for UINT16_MAX we do need some explanation too, right?
>while as it is now it's clearly a placeholder $BIGNUM.
>=20
> /Bruce