[ovs-dev] [PATCH v1 branch-2.14 2/2] acinclude: Strip out -mno-avx512f provided by DPDK.

[Ilya Maximets]

On 1/15/21 7:13 PM, Ilya Maximets wrote:
> On 1/15/21 6:38 PM, Ian Stokes wrote:
>> DPDK forces '-mno-avx512f' flag for the application if the toolchain
>> used to build DPDK had broken AVX512 support.
>>
>> DPDK forces '-mno-avx512f' flag for the application if the toolchain
>> used to build DPDK had broken AVX512 support.  But OVS could be built
>> with a completely different or fixed toolchain with correct avx512
>> support.
>>
>> Fix that by stripping out `-mno-avx512f` as we already do for '-march'.
>> This will allow the OVS to decide if the AVX512 can be used.
>>
>> Reordering of CFLAGS (i.e. adding DPDK flags before OVS ones) is not an
>> option since autotools might reorder them back later and it's very
>> unpredictable.
>>
>> Reported-at: openvswitch/ovs-issues#201
> 
> Same here.
> I think, it's better to have a URL here.  Could be changed on commit.
> Otherwise, LGTM.
> 
>> Signed-off-by: Ilya Maximets <i.maximets at ovn.org>
>> Co-authored-by: Ilya Maximets <i.maximets at ovn.org>
>> Signed-off-by: Ian Stokes <ian.stokes at intel.com>
>> ---
>>  acinclude.m4 | 8 +++++++-
>>  1 file changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/acinclude.m4 b/acinclude.m4
>> index 14fe4218a..5710f5da8 100644
>> --- a/acinclude.m4
>> +++ b/acinclude.m4
>> @@ -438,7 +438,13 @@ AC_DEFUN([OVS_CHECK_DPDK], [
>>      fi
>>      # Force in pkg-config since this could override user-specified options.
>>      # It's enough to have -mssse3 to build with DPDK headers.
>> -    DPDK_INCLUDE=$(echo "$DPDK_INCLUDE" | sed 's/-march=[[^ ]]*//g')
>> +    DPDK_INCLUDE=$(echo "$DPDK_INCLUDE" | sed 's/-march=[[^ ]]*//g'

OK.  I missed that during the review.

>> +    # Also stripping out '-mno-avx512f'.  Support for AVX512 will be disabled
>> +    # if OVS will detect that it's broken.  OVS could be built with a
>> +    # completely different toolchain that correctly supports AVX512, flags
>> +    # forced by DPDK only breaks our feature detection mechanism and leads to
>> +    # build failures: https://github.com/openvswitch/ovs-issues/issues/201
>> +    DPDK_INCLUDE=$(echo "$DPDK_INCLUDE" | sed 's/-mno-avx512f//g'))
>>      OVS_CFLAGS="$OVS_CFLAGS $DPDK_INCLUDE"
>>      OVS_ENABLE_OPTION([-mssse3])
>>  
>>
>