> -----Original Message-----
> From: Ferriter, Cian
> Sent: Friday 28 January 2022 16:32
> To: William Tu <u9012...@gmail.com>; d...@openvswitch.org
> Subject: RE: [ovs-dev] [PATCH] acinclude: Detect avx512 vpopcntdq compiler
> support.
>
>
> > -----Original Message-----
> > From: dev <ovs-dev-boun...@openvswitch.org> On Behalf Of William Tu
> > Sent: Thursday 27 January 2022 03:45
> > To: d...@openvswitch.org
> > Subject: [ovs-dev] [PATCH] acinclude: Detect avx512 vpopcntdq compiler
> > support.
> >
> > Ubuntu Xenial 16.04 is using GCC 5.4 and it does not support
> > target "-mavx512vpopcntdq" and cuases error
> > lib/dpif-netdev-lookup-avx512-gather.c:356:47:
> > error: attribute(target("avx512vpopcntdq")) is unknown
> > GCC 7+ supports vpopcntdq:
> > https://gcc.gnu.org/gcc-7/changes.html
> > The patch detects vpopcntdq and disables AVX512 when not found.
> >
> > Reported-by: Greg Rose <gvrose8...@gmail.com>
> > Signed-off-by: William Tu <u9012...@gmail.com>
> > ---
> > acinclude.m4 | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/acinclude.m4 b/acinclude.m4
> > index 5c971e98ce91..0c360fd1ef73 100644
> > --- a/acinclude.m4
> > +++ b/acinclude.m4
> > @@ -77,7 +77,7 @@ dnl Checks if compiler and binutils supports AVX512.
> > AC_DEFUN([OVS_CHECK_AVX512], [
> > OVS_CHECK_BINUTILS_AVX512
> > OVS_CHECK_CC_OPTION(
> > - [-mavx512f], [ovs_have_cc_mavx512f=yes], [ovs_have_cc_mavx512f=no])
> > + [-mavx512f -mavx512vpopcntdq], [ovs_have_cc_mavx512f=yes],
> > [ovs_have_cc_mavx512f=no])
> > AM_CONDITIONAL([HAVE_AVX512F], [test $ovs_have_cc_mavx512f = yes])
> > if test "$ovs_have_cc_mavx512f" = yes; then
> > AC_DEFINE([HAVE_AVX512F], [1],
> > --
>
> Hi William,
>
> Thanks for this fix, I can verify that this fixes the below error for GCC 5
> (it will work for GCC 4.9
> - GCC 6):
> make[3]: Entering directory '/root/cian/ovs/datapath'
> lib/dpif-netdev-lookup-avx512-gather.c:90:1: error:
> attribute(target("avx512vpopcntdq")) is unknown
>
> We would like to re-spin a new version of this patch that fixes the compile
> error for the relevant GCC
> versions (GCC 4.9 - GCC 6) but allows some AVX512 code to be build.
> For setups with GCC 6 for example, we still have support for most of the
> AVX512 ISA used in OVS, so we
> can still enable building of this ISA, while still correctly avoiding the
> avx512vpopcntdq error that
> your patch does.
>
> Please allow us a few days to test and re-spin a new version of this patch.
> Thanks,
> Cian
Hi again William,
I have been looking into a new version of this patch to add partial support to
GCC versions that don't have full support for all the AVX512 ISA we use in OVS.
This is still a work in progress.
While I'm looking into this more, I think it doesn't make sense to hold back
this patch from being merged. It fixes build issues.
I think the patch should be applied as is. We can add further improvements
later.
Acked-by: Cian Ferriter <cian.ferri...@intel.com>
More details about what I tested:
I switched to GCC 5 on my system and can see the compile issue below before
applying the patch.
After applying the patch, the build is successful.
Before patch
Configure message:
checking whether gcc accepts -mavx512f... yes
Build error:
make[3]: Entering directory '/root/cian/ovs/datapath'
lib/dpif-netdev-lookup-avx512-gather.c:90:1: error:
attribute(target("avx512vpopcntdq")) is unknown
After patch
Configure message:
checking whether gcc accepts -mavx512f -mavx512vpopcntdq... no
On GCC 4.8 before the patch is applied, the build is actually successful, since
the "avx512f" only check fails, so the AVX512 build is disabled.
On GCC 4.8 after the patch is applied, the build still works as expected.
Before patch
Configure message:
checking whether gcc -std=gnu99 accepts -mavx512f... no
After patch
Configure message:
checking whether gcc -std=gnu99 accepts -mavx512f -mavx512vpopcntdq... no
I also checked that all was working as expected with the compile time AVX512
flags:
--enable-dpif-default-avx512 --enable-autovalidator
--enable-mfex-default-autovalidator
I can confirm that these compile time flags don't cause issues.
Finally, I tested and confirmed that OVS was still building and running with
AVX512 support when built with GCC 9.
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