On 8/10/21 12:11 PM, Stokes, Ian wrote:
>>> -----Original Message-----
>>> From: Van Haaren, Harry <[email protected]>
>>> Sent: Thursday, July 29, 2021 5:55 PM
>>> To: [email protected]
>>> Cc: Stokes, Ian <[email protected]>; Van Haaren, Harry
>>> <[email protected]>
>>> Subject: [PATCH] dpcls: fix build on compilers without AVX512-VPOPCNT
>>>
>>> This commit adds extra checks around the AVX-512 vpopcnt instruction
>>> enabling, ensuring that in the function where the ISA is enabled the
>>> compiler has also indicated its support for the ISA. This is achieved
>>> by checking the __AVX512VPOPCNTDQ__ define, which the compiler sets if
>>> it is capable of handling the vpopcnt instruction.
>>>
>>> If the compiler is not capable of handling vpopcnt, we fall back to
>>> the emulated vpopcnt implementation.
>>>
>>> Reported-by: Ian Stokes <[email protected]>
>>> Signed-off-by: Harry van Haaren <[email protected]>
>>>
>>> ---
>>>
>>> Based on a very old system with GCC 7, an issue was identified
>>> where the compiler doesn't support the vpopcnt ISA, and resulted
>>> in compilation failures.
>>
>> Ping on this patch, would be good to get integrated on 2.16 and master to
>> ensure Gcc7 builds correctly.
>
> HI Harry,
>
> Just testing this now.
>
> Regards
> Ian
FWIW,
I tried to test this yesterday, but I realized that you need gcc 7.0.0
for this, because AVX512VPOPCNTDQ is supported starting 7.0.1.
That's a very weird system you have. :)
Unfortunately, I realized this too late when I already built 7.5.0 from
sources and I didn't want to waste another 40 mins building 7.0.0.
So, I carved out support for AVX512VPOPCNTDQ from gcc 7.5.0.
In this configuration it failed to build OVS with the following error:
lib/dpif-netdev-lookup-avx512-gather.c: In function
‘_mm512_popcnt_epi64_wrapper’:
lib/dpif-netdev-lookup-avx512-gather.c:62:12: error: implicit declaration of
function ‘_mm512_popcnt_epi64’; did you mean ‘_mm512_lzcnt_epi64’?
[-Werror=implicit-function-declaration]
return _mm512_popcnt_epi64(v_in);
^~~~~~~~~~~~~~~~~~~
_mm512_lzcnt_epi64
With the patch applied, this modified gcc was able to build OVS
successfully.
Best regards, Ilya Maximets.
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