[ovs-dev] [PATCH v1] configure: Allow opt-in to CPU ISA opts at compile time

Wed Sep 8 08:15:41 UTC 2021

Not a real review of the patch, but just some comment/questions glancing over the patch.

On 3 Sep 2021, at 15:53, Kumar Amber wrote:

> This commit allows "opt-in" to CPU ISA optimized implementations of
> OVS SW datapath components at compile time. This can be useful in some
> deployments where the CPU ISA optimized implementation is to be chosen
> by default.
>
> If an subtable implementation is not available due to ISA not being available,
> it will not be selected.
>
> With --enable-cpu-isa on an AVX512 capable CPU, the dpcls_avx512_gather,
> the DPIF AVX512, MFEX AVX512 ISA optimized implementation is automatically
> enabled.
>
> The default is off, so unless ./configure --enable-cpu-isa is passed,
> the behaviour of the default OVS compile is not changed.
>
> Signed-off-by: Kumar Amber <kumar.amber at intel.com>
> Signed-off-by: Harry van Haaren <harry.van.haaren at intel.com>
> Co-authored-by: Harry van Haaren <harry.van.haaren at intel.com>
> ---
>  Documentation/topics/dpdk/bridge.rst |  9 +++++++++
>  NEWS                                 |  2 ++
>  acinclude.m4                         | 17 +++++++++++++++++
>  configure.ac                         |  1 +
>  lib/dpif-netdev-lookup.c             |  8 +++++++-
>  lib/dpif-netdev-private-dpif.c       |  2 +-
>  lib/dpif-netdev-private-extract.c    |  2 ++
>  7 files changed, 39 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/topics/dpdk/bridge.rst b/Documentation/topics/dpdk/bridge.rst
> index f645b9ade..8568ec365 100644
> --- a/Documentation/topics/dpdk/bridge.rst
> +++ b/Documentation/topics/dpdk/bridge.rst
> @@ -436,3 +436,12 @@ the following test-case in tests/system-dpdk.at ::
>
>      make check-dpdk TESTSUITEFLAGS='-k MFEX'
>      OVS-DPDK - MFEX Autovalidator Fuzzy
> +
> +Enabling all AVX512 options
> +---------------------------
> +
> +A user can enable all the three DPIF, Miniflow Extract and DPLCS optimized
> +AVX512 options at build time, if the CPU supports the required AVX512 ISA
> +by using the following command ::
> +
> +    ./configure --enable-cpu-isa

If we have different ISA architectures, i.e., i86 vs ARM, we are ok with a single option. Have you thought about AMD adding its own AMDXXX instructions in addition to AVX512? How would this configuration option work? Maybe an optional option to prioritize one over the other.

Even if we decide a single option is right, this one to me looks more about compile-time flags than enable ISA-specific code. Maybe something more in line with --prioritize-cpu-isa-functions? Or some other catchy name.

> diff --git a/NEWS b/NEWS
> index 1f2adf718..8d700595b 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -68,6 +68,8 @@ v2.16.0 - 16 Aug 2021
>       * Add new 'pmd-rxq-isolate' option that can be set to 'false' in order
>         that pmd cores which are pinned with rxqs using 'pmd-rxq-affinity'
>         are available for assigning other non-pinned rxqs.
> +     * Add command and documentation to enable all AVX512 optimized options
> +       by default at build time.
>     - ovs-ctl:
>       * New option '--no-record-hostname' to disable hostname configuration
>         in ovsdb on startup.
> diff --git a/acinclude.m4 b/acinclude.m4
> index dba365ea1..75098f980 100644
> --- a/acinclude.m4
> +++ b/acinclude.m4
> @@ -33,6 +33,23 @@ AC_DEFUN([OVS_CHECK_MFEX_AUTOVALIDATOR], [
>    fi
>  ])
>
> +dnl Set OVS DPCLS DPIF and MFEX to AVX512 opt at compile time?
> +AC_DEFUN([OVS_CHECK_CPU_ISA_OPT_IN], [
> +  AC_ARG_ENABLE([cpu-isa],
> +                [AC_HELP_STRING([--enable-cpu-isa],
> +                [Enable CPU ISA default enable.])],
> +                [isa=yes],[isa=no])
> +  AC_MSG_CHECKING([whether CPU ISA should be enabled by default])

This description does not sound right?

> +  if test "$isa" != yes; then
> +    AC_MSG_RESULT([no])
> +  else
> +    AC_DEFINE([CPU_ISA_OPT_IN], [1],
> +              [DPIF AVX512, DPCLS AVX512, MFEX AVX512 is a
> +               default implementation.])
> +    AC_MSG_RESULT([yes])
> +  fi
> +])
> +
>  dnl Set OVS DPCLS Autovalidator as default subtable search at compile time?
>  dnl This enables automatically running all unit tests with all DPCLS
>  dnl implementations.
> diff --git a/configure.ac b/configure.ac
> index eaa9bf7ee..47e64a98c 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -182,6 +182,7 @@ OVS_CONDITIONAL_CC_OPTION([-Wno-unused-parameter], [HAVE_WNO_UNUSED_PARAMETER])
>  OVS_ENABLE_WERROR
>  OVS_ENABLE_SPARSE
>  OVS_CTAGS_IDENTIFIERS
> +OVS_CHECK_CPU_ISA_OPT_IN
>  OVS_CHECK_DPCLS_AUTOVALIDATOR
>  OVS_CHECK_DPIF_AVX512_DEFAULT
>  OVS_CHECK_MFEX_AUTOVALIDATOR
> diff --git a/lib/dpif-netdev-lookup.c b/lib/dpif-netdev-lookup.c
> index bd0a99abe..0989c6a5f 100644
> --- a/lib/dpif-netdev-lookup.c
> +++ b/lib/dpif-netdev-lookup.c
> @@ -45,7 +45,13 @@ static struct dpcls_subtable_lookup_info_t subtable_lookups[] = {
>
>  #if (__x86_64__ && HAVE_AVX512F && HAVE_LD_AVX512_GOOD && __SSE4_2__)
>      /* Only available on x86_64 bit builds with SSE 4.2 used for OVS core. */
> -    { .prio = 0,
> +    {
> +#ifdef CPU_ISA_OPT_IN
> +      /* Allow Autovalidator to override, but higher than default scalar. */
> +      .prio = 100,
> +#else
> +      .prio = 0,
> +#endif
>        .probe = dpcls_subtable_avx512_gather_probe,
>        .name = "avx512_gather", },
>  #else
> diff --git a/lib/dpif-netdev-private-dpif.c b/lib/dpif-netdev-private-dpif.c
> index 84d4ec156..22761c10e 100644
> --- a/lib/dpif-netdev-private-dpif.c
> +++ b/lib/dpif-netdev-private-dpif.c
> @@ -60,7 +60,7 @@ dp_netdev_impl_get_default(void)
>
>  /* Configure-time overriding to run test suite on all implementations. */
>  #if (__x86_64__ && HAVE_AVX512F && HAVE_LD_AVX512_GOOD && __SSE4_2__)
> -#ifdef DPIF_AVX512_DEFAULT
> +#if defined(DPIF_AVX512_DEFAULT) || defined(CPU_ISA_OPT_IN)
>          dp_netdev_input_func_probe probe;
>
>          /* Check if the compiled default is compatible. */
> diff --git a/lib/dpif-netdev-private-extract.c b/lib/dpif-netdev-private-extract.c
> index 7a06dbf6f..482aa1f37 100644
> --- a/lib/dpif-netdev-private-extract.c
> +++ b/lib/dpif-netdev-private-extract.c
> @@ -105,6 +105,8 @@ dpif_miniflow_extract_init(void)
>      atomic_uintptr_t *mfex_func = (void *)&default_mfex_func;
>  #ifdef MFEX_AUTOVALIDATOR_DEFAULT
>      int mfex_idx = MFEX_IMPL_AUTOVALIDATOR;
> +#elif CPU_ISA_OPT_IN
> +    int mfex_idx = MFEX_IMPL_STUDY;
>  #else
>      int mfex_idx = MFEX_IMPL_SCALAR;
>  #endif
> -- 
> 2.25.1