[RFC PATCH] build: reduce use of AVX compiler flags

[RFC PATCH] build: reduce use of AVX compiler flags

[Bruce Richardson]

When doing a build for a target that already has the instruction sets
for AVX2/AVX512 enabled, skip emitting the AVX compiler flags, or the
skylake-avx512 '-march' flags, as they are unnecessary. Instead, when
the default flags produce the desired output, just use them unmodified.

Depends-on: series-34915 ("remove component-specific logic for AVX builds")

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
---

This patchset depends on the previous AVX rework. However, sending it
separately as a new RFC because it effectively increases the minimum
compiler versions needed for x86 builds - from GCC 5 to 6, and
Clang 3.6 to 3.9.

For now, I've just documented that as an additional note in the GSG that
these versions are recommended, but it would be simpler if we could just
set them as the required minimum baseline (at least in the docs).

Feedback on these compiler version requirements welcome.

---
 config/x86/meson.build            | 31 ++++++++++++++++++++-----------
 doc/guides/linux_gsg/sys_reqs.rst |  8 ++++++++
 drivers/meson.build               |  9 +--------
 lib/meson.build                   |  9 +--------
 4 files changed, 30 insertions(+), 27 deletions(-)

diff --git a/config/x86/meson.build b/config/x86/meson.build
index c3564b0011..97f790b0d4 100644
--- a/config/x86/meson.build
+++ b/config/x86/meson.build
@@ -4,11 +4,13 @@
 if is_ms_compiler
     cc_avx2_flags = ['/arch:AVX2']
 else
-    cc_avx2_flags = ['-mavx2']
+    cc_avx2_flags = []
+    if cc.get_define('__AVX2__', args: machine_args) == ''
+        cc_avx2_flags = ['-mavx2']
+    endif
 endif

 cc_has_avx512 = false
-target_has_avx512 = false

 dpdk_conf.set('RTE_ARCH_X86', 1)
 if dpdk_conf.get('RTE_ARCH_64')
@@ -65,26 +67,33 @@ if is_linux or cc.get_id() == 'gcc'
     endif
 endif

-cc_avx512_flags = ['-mavx512f', '-mavx512vl', '-mavx512dq', '-mavx512bw', '-mavx512cd']
-if (binutils_ok and cc.has_multi_arguments(cc_avx512_flags)
+avx512_march_flag = '-march=skylake-avx512'
+cc_avx512_flags = []
+if (binutils_ok and cc.has_argument(avx512_march_flag)
         and '-mno-avx512f' not in get_option('c_args'))
     # check if compiler is working with _mm512_extracti64x4_epi64
     # Ref: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82887
     code = '''#include <immintrin.h>
     void test(__m512i zmm){
         __m256i ymm = _mm512_extracti64x4_epi64(zmm, 0);}'''
-    result = cc.compiles(code, args : cc_avx512_flags, name : 'AVX512 checking')
+    result = cc.compiles(code, args : [avx512_march_flag], name : 'AVX512 checking')
     if result == false
         machine_args += '-mno-avx512f'
         warning('Broken _mm512_extracti64x4_epi64, disabling AVX512 support')
     else
         cc_has_avx512 = true
-        target_has_avx512 = (
-                cc.get_define('__AVX512F__', args: machine_args) != '' and
-                cc.get_define('__AVX512BW__', args: machine_args) != '' and
-                cc.get_define('__AVX512DQ__', args: machine_args) != '' and
-                cc.get_define('__AVX512VL__', args: machine_args) != ''
-            )
+        if cc.get_define('__AVX512F__', args: machine_args) == ''
+            cc_avx512_flags = [avx512_march_flag]
+            if cc.has_argument('-Wno-overriding-option')
+                cc_avx512_args += '-Wno-overriding-option'
+            endif
+        endif
+    endif
+endif
+if developer_mode
+    message('Extra C flags needed for AVX2 output: @0@'.format(cc_avx2_flags))
+    if cc_has_avx512
+        message('Extra C flags needed for AVX512 output: @0@'.format(cc_avx512_flags))
     endif
 endif

diff --git a/doc/guides/linux_gsg/sys_reqs.rst b/doc/guides/linux_gsg/sys_reqs.rst
index 5a7d9e4a43..55e9fe4724 100644
--- a/doc/guides/linux_gsg/sys_reqs.rst
+++ b/doc/guides/linux_gsg/sys_reqs.rst
@@ -35,6 +35,14 @@ Compilation of the DPDK
     * For Ubuntu/Debian systems these can be installed using ``apt install build-essential``
     * For Alpine Linux, ``apk add alpine-sdk bsd-compat-headers``

+.. note::
+
+   When compiling for x86 platforms,
+   GCC version 6.1 or higher,
+   or Clang version 3.9 or higher is recommended.
+   Earlier versions of these compilers do not support the compiler flags used by DPDK for AVX-512 code.
+   As such, any builds using earlier compilers will be missing AVX-512 support.
+
 .. note::

    pkg-config 0.27, supplied with RHEL-7,
diff --git a/drivers/meson.build b/drivers/meson.build
index c15319dc24..bb33b0a7a0 100644
--- a/drivers/meson.build
+++ b/drivers/meson.build
@@ -249,18 +249,11 @@ foreach subpath:subdirs
             endif
             if sources_avx512.length() > 0 and cc_has_avx512
                 cflags += '-DCC_AVX512_SUPPORT'
-                avx512_args = [cflags, cc_avx512_flags]
-                if not target_has_avx512 and cc.has_argument('-march=skylake-avx512')
-                    avx512_args += '-march=skylake-avx512'
-                    if cc.has_argument('-Wno-overriding-option')
-                        avx512_args += '-Wno-overriding-option'
-                    endif
-                endif
                 avx512_lib = static_library(lib_name + '_avx512_lib',
                         sources_avx512,
                         dependencies: static_deps,
                         include_directories: includes,
-                        c_args: avx512_args)
+                        c_args: [cflags, cc_avx512_flags])
                 objs += avx512_lib.extract_objects(sources_avx512)
             endif
         endif
diff --git a/lib/meson.build b/lib/meson.build
index e2605e7d68..887e0ed56d 100644
--- a/lib/meson.build
+++ b/lib/meson.build
@@ -257,18 +257,11 @@ foreach l:libraries
         endif
         if sources_avx512.length() > 0 and cc_has_avx512
             cflags += '-DCC_AVX512_SUPPORT'
-            avx512_args = [cflags, cflags_avx512, cc_avx512_flags]
-            if not target_has_avx512 and cc.has_argument('-march=skylake-avx512')
-                avx512_args += '-march=skylake-avx512'
-                if cc.has_argument('-Wno-overriding-option')
-                    avx512_args += '-Wno-overriding-option'
-                endif
-            endif
             avx512_lib = static_library(libname + '_avx512_lib',
                     sources_avx512,
                     dependencies: static_deps,
                     include_directories: includes,
-                    c_args: avx512_args)
+                    c_args: [cflags, cflags_avx512, cc_avx512_flags])
             objs += avx512_lib.extract_objects(sources_avx512)
         endif
     endif
--
2.45.2

Re: [RFC PATCH] build: reduce use of AVX compiler flags

[Bruce Richardson]

On Tue, Mar 25, 2025 at 05:22:15PM +0000, Bruce Richardson wrote:
> When doing a build for a target that already has the instruction sets
> for AVX2/AVX512 enabled, skip emitting the AVX compiler flags, or the
> skylake-avx512 '-march' flags, as they are unnecessary. Instead, when
> the default flags produce the desired output, just use them unmodified.
> 
> Depends-on: series-34915 ("remove component-specific logic for AVX builds")
> 
> Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> ---
> 
> This patchset depends on the previous AVX rework. However, sending it
> separately as a new RFC because it effectively increases the minimum
> compiler versions needed for x86 builds - from GCC 5 to 6, and
> Clang 3.6 to 3.9.
> 
> For now, I've just documented that as an additional note in the GSG that
> these versions are recommended, but it would be simpler if we could just
> set them as the required minimum baseline (at least in the docs).
> 
> Feedback on these compiler version requirements welcome.
>

+techboard

Ping for a little bit of feedback for this. Are we ok to bump the minimum
compiler versions as described above, or will I continue with the approach
in this RFC of keeping the minimum and just recommending the higher
versions for x86 platforms?

For reference GCC 6.1 was released April 2016[1], and, Clang 3.9 was
released Sept 2016[2]

/Bruce

[1] https://gcc.gnu.org/gcc-6/
[2] https://releases.llvm.org/

RE: [RFC PATCH] build: reduce use of AVX compiler flags

[Morten Brørup]

> From: Bruce Richardson [mailto:bruce.richardson@intel.com]
> Sent: Wednesday, 26 March 2025 17.22
> 
> On Tue, Mar 25, 2025 at 05:22:15PM +0000, Bruce Richardson wrote:
> > When doing a build for a target that already has the instruction sets
> > for AVX2/AVX512 enabled, skip emitting the AVX compiler flags, or the
> > skylake-avx512 '-march' flags, as they are unnecessary. Instead, when
> > the default flags produce the desired output, just use them
> unmodified.
> >
> > Depends-on: series-34915 ("remove component-specific logic for AVX
> builds")
> >
> > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> > ---
> >
> > This patchset depends on the previous AVX rework. However, sending it
> > separately as a new RFC because it effectively increases the minimum
> > compiler versions needed for x86 builds - from GCC 5 to 6, and
> > Clang 3.6 to 3.9.
> >
> > For now, I've just documented that as an additional note in the GSG
> that
> > these versions are recommended, but it would be simpler if we could
> just
> > set them as the required minimum baseline (at least in the docs).
> >
> > Feedback on these compiler version requirements welcome.
> >
> 
> +techboard
> 
> Ping for a little bit of feedback for this. Are we ok to bump the
> minimum
> compiler versions as described above, or will I continue with the
> approach
> in this RFC of keeping the minimum and just recommending the higher
> versions for x86 platforms?
> 
> For reference GCC 6.1 was released April 2016[1], and, Clang 3.9 was
> released Sept 2016[2]
> 
> /Bruce
> 
> [1] https://gcc.gnu.org/gcc-6/
> [2] https://releases.llvm.org/

Considering GCC versions shipped with RHEL [3]...
We kind of support RHEL 7, but we already require a newer compiler (GCC 5) than shipped with RHEL 7 (GCC 4.8).
RHEL 8 ships with GCC 8, which was released in May 2018 [4]. Maybe we can jump to GCC 8?

BTW, we should also apply the same principle I argued [5] should apply for upgrading the Kernel requirements: There should be a need for specific feature or similar - which there is with your patch - and the details should be mentioned in the release notes.

[3]: https://access.redhat.com/solutions/19458
[4]: https://gcc.gnu.org/gcc-8/
[5]: https://inbox.dpdk.org/dev/CAMEVEZutf4sJ=EQFONw_bJW0tGTWqTbF_Tk_y38qzBLccco46Q@mail.gmail.com/T/#me7c8f1dbe4331ccf232d43512d6ddb51458c568a

Re: [RFC PATCH] build: reduce use of AVX compiler flags

[Stephen Hemminger]

On Wed, 26 Mar 2025 19:06:58 +0100
Morten Brørup <mb@smartsharesystems.com> wrote:

> > From: Bruce Richardson [mailto:bruce.richardson@intel.com]
> > Sent: Wednesday, 26 March 2025 17.22
> > 
> > On Tue, Mar 25, 2025 at 05:22:15PM +0000, Bruce Richardson wrote:  
> > > When doing a build for a target that already has the instruction sets
> > > for AVX2/AVX512 enabled, skip emitting the AVX compiler flags, or the
> > > skylake-avx512 '-march' flags, as they are unnecessary. Instead, when
> > > the default flags produce the desired output, just use them  
> > unmodified.  
> > >
> > > Depends-on: series-34915 ("remove component-specific logic for AVX  
> > builds")  
> > >
> > > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> > > ---
> > >
> > > This patchset depends on the previous AVX rework. However, sending it
> > > separately as a new RFC because it effectively increases the minimum
> > > compiler versions needed for x86 builds - from GCC 5 to 6, and
> > > Clang 3.6 to 3.9.
> > >
> > > For now, I've just documented that as an additional note in the GSG  
> > that  
> > > these versions are recommended, but it would be simpler if we could  
> > just  
> > > set them as the required minimum baseline (at least in the docs).
> > >
> > > Feedback on these compiler version requirements welcome.
> > >  
> > 
> > +techboard
> > 
> > Ping for a little bit of feedback for this. Are we ok to bump the
> > minimum
> > compiler versions as described above, or will I continue with the
> > approach
> > in this RFC of keeping the minimum and just recommending the higher
> > versions for x86 platforms?
> > 
> > For reference GCC 6.1 was released April 2016[1], and, Clang 3.9 was
> > released Sept 2016[2]
> > 
> > /Bruce
> > 
> > [1] https://gcc.gnu.org/gcc-6/
> > [2] https://releases.llvm.org/  
> 
> Considering GCC versions shipped with RHEL [3]...
> We kind of support RHEL 7, but we already require a newer compiler (GCC 5) than shipped with RHEL 7 (GCC 4.8).
> RHEL 8 ships with GCC 8, which was released in May 2018 [4]. Maybe we can jump to GCC 8?
> 
> BTW, we should also apply the same principle I argued [5] should apply for upgrading the Kernel requirements: There should be a need for specific feature or similar - which there is with your patch - and the details should be mentioned in the release notes.
> 
> [3]: https://access.redhat.com/solutions/19458
> [4]: https://gcc.gnu.org/gcc-8/
> [5]: https://inbox.dpdk.org/dev/CAMEVEZutf4sJ=EQFONw_bJW0tGTWqTbF_Tk_y38qzBLccco46Q@mail.gmail.com/T/#me7c8f1dbe4331ccf232d43512d6ddb51458c568a
> 

RHEL 7 reached end of life on June 30, 2024.
DPDK need no longer support it on future versions.

DPDK compilers and RHEL 7 support

[Morten Brørup]

+ Red Hat tech board members

> From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> Sent: Wednesday, 26 March 2025 20.21
> 
> On Wed, 26 Mar 2025 19:06:58 +0100
> Morten Brørup <mb@smartsharesystems.com> wrote:
> 
> > > From: Bruce Richardson [mailto:bruce.richardson@intel.com]
> > > Sent: Wednesday, 26 March 2025 17.22
> > >
> > > On Tue, Mar 25, 2025 at 05:22:15PM +0000, Bruce Richardson wrote:
> > > > When doing a build for a target that already has the instruction
> sets
> > > > for AVX2/AVX512 enabled, skip emitting the AVX compiler flags, or
> the
> > > > skylake-avx512 '-march' flags, as they are unnecessary. Instead,
> when
> > > > the default flags produce the desired output, just use them
> > > unmodified.
> > > >
> > > > Depends-on: series-34915 ("remove component-specific logic for
> AVX
> > > builds")
> > > >
> > > > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> > > > ---
> > > >
> > > > This patchset depends on the previous AVX rework. However,
> sending it
> > > > separately as a new RFC because it effectively increases the
> minimum
> > > > compiler versions needed for x86 builds - from GCC 5 to 6, and
> > > > Clang 3.6 to 3.9.
> > > >
> > > > For now, I've just documented that as an additional note in the
> GSG
> > > that
> > > > these versions are recommended, but it would be simpler if we
> could
> > > just
> > > > set them as the required minimum baseline (at least in the docs).
> > > >
> > > > Feedback on these compiler version requirements welcome.
> > > >
> > >
> > > +techboard
> > >
> > > Ping for a little bit of feedback for this. Are we ok to bump the
> > > minimum
> > > compiler versions as described above, or will I continue with the
> > > approach
> > > in this RFC of keeping the minimum and just recommending the higher
> > > versions for x86 platforms?
> > >
> > > For reference GCC 6.1 was released April 2016[1], and, Clang 3.9
> was
> > > released Sept 2016[2]
> > >
> > > /Bruce
> > >
> > > [1] https://gcc.gnu.org/gcc-6/
> > > [2] https://releases.llvm.org/
> >
> > Considering GCC versions shipped with RHEL [3]...
> > We kind of support RHEL 7, but we already require a newer compiler
> (GCC 5) than shipped with RHEL 7 (GCC 4.8).
> > RHEL 8 ships with GCC 8, which was released in May 2018 [4]. Maybe we
> can jump to GCC 8?
> >
> > BTW, we should also apply the same principle I argued [5] should
> apply for upgrading the Kernel requirements: There should be a need for
> specific feature or similar - which there is with your patch - and the
> details should be mentioned in the release notes.
> >
> > [3]: https://access.redhat.com/solutions/19458
> > [4]: https://gcc.gnu.org/gcc-8/
> > [5]:
> https://inbox.dpdk.org/dev/CAMEVEZutf4sJ=EQFONw_bJW0tGTWqTbF_Tk_y38qzBL
> ccco46Q@mail.gmail.com/T/#me7c8f1dbe4331ccf232d43512d6ddb51458c568a
> >
> 
> RHEL 7 reached end of life on June 30, 2024.
> DPDK need no longer support it on future versions.

CentOS 7 reached EOL June 2024, yes.
RHEL 7 reached End of Maintenance June 2024, but RHEL 7 Extended Life Cycle Support is available until June 2028 [6].

Although RHEL 7 not fully EOL, I would consider "End Of Maintenance" sufficiently dead for future DPDK versions not needing to support it.
If you are running a production system on a distro that's on Extended Life Cycle Support, you shouldn't deploy a new DPDK version - and if you do anyway, it's your own problem, not the DPDK community's problem.
@Aaron, @Kevin, @Maxime - speak up if you disagree!


[6]: https://www.redhat.com/en/technologies/linux-platforms/enterprise-linux/rhel-7-end-of-maintenance

Re: DPDK compilers and RHEL 7 support

[Kevin Traynor]

On 27/03/2025 07:55, Morten Brørup wrote:
> + Red Hat tech board members
> 
>> From: Stephen Hemminger [mailto:stephen@networkplumber.org]
>> Sent: Wednesday, 26 March 2025 20.21
>>
>> On Wed, 26 Mar 2025 19:06:58 +0100
>> Morten Brørup <mb@smartsharesystems.com> wrote:
>>
>>>> From: Bruce Richardson [mailto:bruce.richardson@intel.com]
>>>> Sent: Wednesday, 26 March 2025 17.22
>>>>
>>>> On Tue, Mar 25, 2025 at 05:22:15PM +0000, Bruce Richardson wrote:
>>>>> When doing a build for a target that already has the instruction
>> sets
>>>>> for AVX2/AVX512 enabled, skip emitting the AVX compiler flags, or
>> the
>>>>> skylake-avx512 '-march' flags, as they are unnecessary. Instead,
>> when
>>>>> the default flags produce the desired output, just use them
>>>> unmodified.
>>>>>
>>>>> Depends-on: series-34915 ("remove component-specific logic for
>> AVX
>>>> builds")
>>>>>
>>>>> Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
>>>>> ---
>>>>>
>>>>> This patchset depends on the previous AVX rework. However,
>> sending it
>>>>> separately as a new RFC because it effectively increases the
>> minimum
>>>>> compiler versions needed for x86 builds - from GCC 5 to 6, and
>>>>> Clang 3.6 to 3.9.
>>>>>
>>>>> For now, I've just documented that as an additional note in the
>> GSG
>>>> that
>>>>> these versions are recommended, but it would be simpler if we
>> could
>>>> just
>>>>> set them as the required minimum baseline (at least in the docs).
>>>>>
>>>>> Feedback on these compiler version requirements welcome.
>>>>>
>>>>
>>>> +techboard
>>>>
>>>> Ping for a little bit of feedback for this. Are we ok to bump the
>>>> minimum
>>>> compiler versions as described above, or will I continue with the
>>>> approach
>>>> in this RFC of keeping the minimum and just recommending the higher
>>>> versions for x86 platforms?
>>>>
>>>> For reference GCC 6.1 was released April 2016[1], and, Clang 3.9
>> was
>>>> released Sept 2016[2]
>>>>
>>>> /Bruce
>>>>
>>>> [1] https://gcc.gnu.org/gcc-6/
>>>> [2] https://releases.llvm.org/
>>>
>>> Considering GCC versions shipped with RHEL [3]...
>>> We kind of support RHEL 7, but we already require a newer compiler
>> (GCC 5) than shipped with RHEL 7 (GCC 4.8).
>>> RHEL 8 ships with GCC 8, which was released in May 2018 [4]. Maybe we
>> can jump to GCC 8?
>>>
>>> BTW, we should also apply the same principle I argued [5] should
>> apply for upgrading the Kernel requirements: There should be a need for
>> specific feature or similar - which there is with your patch - and the
>> details should be mentioned in the release notes.
>>>
>>> [3]: https://access.redhat.com/solutions/19458
>>> [4]: https://gcc.gnu.org/gcc-8/
>>> [5]:
>> https://inbox.dpdk.org/dev/CAMEVEZutf4sJ=EQFONw_bJW0tGTWqTbF_Tk_y38qzBL
>> ccco46Q@mail.gmail.com/T/#me7c8f1dbe4331ccf232d43512d6ddb51458c568a
>>>
>>
>> RHEL 7 reached end of life on June 30, 2024.
>> DPDK need no longer support it on future versions.
> 
> CentOS 7 reached EOL June 2024, yes.
> RHEL 7 reached End of Maintenance June 2024, but RHEL 7 Extended Life Cycle Support is available until June 2028 [6].
> 
> Although RHEL 7 not fully EOL, I would consider "End Of Maintenance" sufficiently dead for future DPDK versions not needing to support it.
> If you are running a production system on a distro that's on Extended Life Cycle Support, you shouldn't deploy a new DPDK version - and if you do anyway, it's your own problem, not the DPDK community's problem.
> @Aaron, @Kevin, @Maxime - speak up if you disagree!
> 

+1

Red Hat will not release new RHEL 7 DPDK packages now and there are no
new features/versions of RHEL 7.

I agree if anyone is running RHEL(/CentOS) 7 at this point, they should
not expect that they can just use new versions of DPDK on it without
having to resolve the dependencies themselves.

> 
> [6]: https://www.redhat.com/en/technologies/linux-platforms/enterprise-linux/rhel-7-end-of-maintenance
>