On 5/18/2021 5:12 PM, Honnappa Nagarahalli wrote:

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<snip>

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On 5/14/2021 10:53 AM, Chengwen Feng wrote:

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Currently, the SVE code is compiled only when -march supports SVE
(e.g. '-march=armv8.2a+sve'), there maybe some problem[1] with this
approach.

The solution:
a. If the minimum instruction set support SVE then compiles it.
b. Else if the compiler support SVE then compiles it.
c. Otherwise don't compile it.

[1] https://mails.dpdk.org/archives/dev/2021-April/208189.html

Hi Chengwen,

As far as I understand from above problem statement, you want to
produce a binary that can run in two different platforms, one
supports only NEON instructions, other supports NEON + SVE.

For this driver should be compiled in a way to support min
instruction set, which is NEON.

There are two build items,

1) hns3_rxtx_vec_sve.c
2) rest of the library

There is already runtime checks to select Rx/Tx functions, so it is
safe to build
(1) as long as compiler supports. If the platform doesn't support
SVE, the SVE path won't be selected during runtime.

For (2), it should be build to support NEON only, if it is compiled
to support SVE, it won't run on the platform that only supports NEON.

So, in below, if '__ARM_FEATURE_SVE' is supported, all driver is
build with SVE support, won't this cause a problem on the NEON platform?

The first if statement checks if the user has enabled SVE during compilation

which indicates that the user will run the binary on a platform that has SVE
(the minimum ISA level supported by this binary), hence it is ok to compile all
the code with SVE.

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So it is related to the what user provided (I assume as compiler flag), instead
of host HW capability.

It is the HW host capability as provided in the compiler flag. It is coming from config/arm/meson.build.

Is this patch has dependency to 1/2, that updates 'config/arm/meson.build'?

What I understand is, if user provides compiler argument to request SVE,
something like '-march=armv8.2-a+sve', and host HW supports it, whole driver
will be built with SVE support.

If user not request SVE, driver won't be compiled with SVE support even if HW
support it, but only 'hns3_rxtx_vec_sve.c' will be compiled if compiler supports
SVE.

Is above correct and does it have any dependency to first patch, I thought this
is independent from first patch.

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If the user has not enabled SVE during compilation which indicates the user

might run the binary on a platform that does not have SVE, the second if
statement, checks if the compiler supports SVE. If yes, it will compile the SVE
version of the driver as well and the run time checks choose the correct
version.

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OK, this sounds good, thanks for clarification.

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What do you think to only keep the else leg of the below check, which
is if compiler supports SVE, set '-DCC_SVE_SUPPORT' flag and only
build (1) with SVE flag?

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Fixes: 8c25b02b082a ("net/hns3: fix enabling SVE Rx/Tx")
Fixes: 952ebacce4f2 ("net/hns3: support SVE Rx")
Cc: stable@dpdk.org

Signed-off-by: Chengwen Feng <redacted>
---
 drivers/net/hns3/hns3_rxtx.c |  2 +-  drivers/net/hns3/meson.build
| 13 +++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/net/hns3/hns3_rxtx.c

b/drivers/net/hns3/hns3_rxtx.c index 1d7a769..4ef20c6 100644

--- a/drivers/net/hns3/hns3_rxtx.c
+++ b/drivers/net/hns3/hns3_rxtx.c

@@ -2808,7 +2808,7 @@ hns3_get_default_vec_support(void)
 static bool
 hns3_get_sve_support(void)
 {
-#if defined(RTE_ARCH_ARM64) && defined(__ARM_FEATURE_SVE)
+#if defined(CC_SVE_SUPPORT)
 	if (rte_vect_get_max_simd_bitwidth() < RTE_VECT_SIMD_256)
 		return false;
 	if (rte_cpu_get_flag_enabled(RTE_CPUFLAG_SVE))

diff --git a/drivers/net/hns3/meson.build

b/drivers/net/hns3/meson.build index 53c7df7..8563d70 100644

--- a/drivers/net/hns3/meson.build
+++ b/drivers/net/hns3/meson.build

@@ -35,7 +35,20 @@ deps += ['hash']

 if arch_subdir == 'arm' and dpdk_conf.get('RTE_ARCH_64')
     sources += files('hns3_rxtx_vec.c')
+
+    # compile SVE when:
+    # a. support SVE in minimum instruction set baseline
+    # b. it's not minimum instruction set, but compiler support
     if cc.get_define('__ARM_FEATURE_SVE', args: machine_args) != ''
+        cflags += ['-DCC_SVE_SUPPORT']
         sources += files('hns3_rxtx_vec_sve.c')
+    elif cc.has_argument('-march=armv8.2-a+sve')
+        cflags += ['-DCC_SVE_SUPPORT']
+        hns3_sve_lib = static_library('hns3_sve_lib',
+                        'hns3_rxtx_vec_sve.c',
+                        dependencies: [static_rte_ethdev],
+                        include_directories: includes,
+                        c_args: [cflags, '-march=armv8.2-a+sve'])
+        objs += hns3_sve_lib.extract_objects('hns3_rxtx_vec_sve.c')
     endif
 endif