Re: [dpdk-dev] [RFC PATCH v2] build: add platform meson option

From: Juraj Linkeš <hidden>
Date: 2021-02-25 12:57:48

-----Original Message-----
From: Bruce Richardson <redacted>
Sent: Thursday, February 25, 2021 1:54 PM
To: Juraj Linkeš <redacted>
Cc: David Christensen <redacted>; thomas@monjalon.net;
Honnappa.Nagarahalli@arm.com; dev@dpdk.org
Subject: Re: [RFC PATCH v2] build: add platform meson option

On Thu, Feb 25, 2021 at 12:51:57PM +0000, Juraj Linkeš wrote:

quoted

-----Original Message-----
From: Bruce Richardson <redacted>
Sent: Tuesday, February 23, 2021 10:43 AM
To: Juraj Linkeš <redacted>
Cc: David Christensen <redacted>; thomas@monjalon.net;
Honnappa.Nagarahalli@arm.com; dev@dpdk.org
Subject: Re: [RFC PATCH v2] build: add platform meson option

On Tue, Feb 23, 2021 at 08:45:09AM +0000, Juraj Linkeš wrote:

quoted

-----Original Message-----
From: David Christensen <redacted>
Sent: Monday, February 22, 2021 10:25 PM
To: Juraj Linkeš <redacted>; Bruce Richardson
[off-list ref]
Cc: thomas@monjalon.net; Honnappa.Nagarahalli@arm.com;

dev@dpdk.org

quoted

Subject: Re: [RFC PATCH v2] build: add platform meson option



On 2/19/21 1:11 AM, Juraj Linkeš wrote:

quoted

-----Original Message-----
From: Bruce Richardson <redacted>
Sent: Wednesday, January 6, 2021 3:43 PM
To: David Christensen <redacted>
Cc: Juraj Linkeš <redacted>;
thomas@monjalon.net; Honnappa.Nagarahalli@arm.com;
dev@dpdk.org
Subject: Re: [RFC PATCH v2] build: add platform meson option

On Tue, Jan 05, 2021 at 02:17:44PM -0800, David Christensen wrote:

quoted

The current meson option 'machine' should only specify the
ISA, which is not sufficient for Arm, where setting ISA
implies other setting as

well.

quoted

Add a new meson option, 'platform', which differentiates
the type of the build
(native/generic) and sets machine accordingly, unless the
user chooses to override it.
The 'machine' option also doesn't describe very well what
it sets, so introduce a new option 'cpu_instruction_set',
but keep 'machine' for backward compatibility.
These two new variables, taken together, achieve what 'machine'
was setting per architecture - setting the ISA in x86
build and setting native/default 'build type' in aarch64
build - is now properly being set for all architectures in a uniform

manner.

quoted

Signed-off-by: Juraj Linkeš <redacted>
---
   config/arm/meson.build        |  4 +--
   config/meson.build            | 47 +++++++++++++++++++++++++----

----

quoted

--

quoted

   devtools/test-meson-builds.sh |  9 ++++---
   meson_options.txt             |  8 ++++--
   4 files changed, 47 insertions(+), 21 deletions(-)

diff --git a/config/arm/meson.build

b/config/arm/meson.build index
42b4e43c7..6b09a74a7 100644

--- a/config/arm/meson.build
+++ b/config/arm/meson.build

@@ -3,10 +3,10 @@
   # Copyright(c) 2017 Cavium, Inc

   # for checking defines we need to use the correct

compiler flags -march_opt = '-
march=@0@'.format(machine)
+march_opt = '-march=@0@'.format(cpu_instruction_set)

   arm_force_native_march = false -arm_force_default_march
= (machine == 'default')
+arm_force_default_march = (platform == 'generic')

   flags_common_default = [
   	# Accelarate rte_memcpy. Be sure to run unit test
(memcpy_perf_autotest) diff --git a/config/meson.build
b/config/meson.build index a3154e29c..647116513 100644

--- a/config/meson.build
+++ b/config/meson.build

@@ -63,42 +63,63 @@ if not is_windows
   			pmd_subdir_opt)
   endif

-# set the machine type and cflags for it
+platform = get_option('platform')
+
+# set the cpu_instruction_set type and cflags for it
   if meson.is_cross_build()
-	machine = host_machine.cpu()
+	cpu_instruction_set = host_machine.cpu()
   else
-	machine = get_option('machine')
+	cpu_instruction_set = get_option('cpu_instruction_set')
+	if get_option('machine') != 'auto'
+		warning('The "machine" option is deprecated. ' +
+		        'Please use "cpu_instruction_set" instead.')
+		if cpu_instruction_set != 'auto'
+			error('Setting both "machine" and ' +
+			      '"cpu_instruction_set" is unsupported.')
+		endif
+		cpu_instruction_set = get_option('machine')
+	endif
+endif
+
+if platform == 'native'
+	if cpu_instruction_set == 'auto'
+		cpu_instruction_set = 'native'
+	endif
+elif platform == 'generic'
+	if cpu_instruction_set == 'auto'
+		cpu_instruction_set = 'default'
+	endif
   endif

-# machine type 'default' is special, it defaults to the

per arch agreed common
+if cpu_instruction_set == 'default'
+# cpu_instruction_set type 'default' is special, it
+defaults to the per arch agreed common
   # minimal baseline needed for DPDK.
   # That might not be the most optimized, but the most
portable version while  # still being able to support the
CPU features required for

DPDK.

quoted

   # This can be bumped up by the DPDK project, but it can
never be an  # invariant like 'native'
-if machine == 'default'
   	if host_machine.cpu_family().startswith('x86')
   		# matches the old pre-meson build systems default
-		machine = 'corei7'
+		cpu_instruction_set = 'corei7'
   	elif host_machine.cpu_family().startswith('arm')
-		machine = 'armv7-a'
+		cpu_instruction_set = 'armv7-a'
   	elif host_machine.cpu_family().startswith('aarch')
   		# arm64 manages defaults in config/arm/meson.build
-		machine = 'default'
+		cpu_instruction_set = 'default'
   	elif host_machine.cpu_family().startswith('ppc')
-		machine = 'power8'
+		cpu_instruction_set = 'power8'
   	endif
   endif

This change forces the build on a P9 system to use the P8 instruction

set.

quoted

Prior to this change the "native" machine type was used
which resulted in P9 instructions when built on a P9 system.
How do I force the build to use the
power9 instruction set in this case?

Dave

 From looking at the patch, setting the "platform" to
"native", or the instruction_set to "native" should do this.
While I consider generic builds a good thing, I wonder if
there is an expectation that "native" is always the default
build type for DPDK

builds?

quoted

/Bruce

I left this patch alone so that people could chime in, but
noone did, so let's try

to find some agreeable solution.

quoted

My current thoughts are as such:
The platform parameter specifies a set of DPDK options that
will be used. This

is what arm uses for its builds, x86 and ppc don't use this.

quoted

The cpu_instruction_set sets just one configuration among the

"platform"

quoted

configuration set.

quoted

We want the build to work on most machines of the machine

architecture.

quoted

That implies platform=generic (as in use config options that
will work on everything of that architecture) and
cpu_instruction_set=generic (as in use ISA that will work on all
cpus of the

build machine architecture).

quoted

Setting cpu_instruction_set=generic changes the build without
cmdline options

for ppc. Thus, the expectation may be that cpu_instruction_set
should be native by default.

quoted

For arm, cpu_instruction_set is ignored (and thus the value
doen't matter),

since we can't use that without other config options (e.g. DPDK
config for an SoC (such as RTE_ARM_FEATURE_ATOMICS) used with an
invalid cpu_instuction_set). That means the only relevant
parameter for Arm is platform and if we want to have a build
usable on most machines of the build type, we have to use

platform=generic.

quoted

For x86 and ppc, there's no difference between native and
generic platform (as

it's a new argument, the purpose of which is to differentiate
DPDK config across platforms, which doesn't exist for x86 and
ppc - DPDK config is the same (correct me if I'm wrong)).

quoted

So it basically boils down to what should be the default value
of

cpu_instruction_set when platform=generic (for platform=native,
it's obviously
native):

quoted

1. cpu_instruction_set=native, this would preserve the current
behavior, but

we won't use the 'auto' default. I think we can fall back to
this if we don't agree on anything better.

quoted

2. cpu_instruction_set=auto, the same as
cpu_instruction_set=generic, 3. cpu_instruction_set=generic,
this changes behavior for ppc builds, but we

may be able to remedy this:

quoted

Similarly to arm (arm is using platform for this, but the idea
is the same), if

cpu_instruction_set is generic, we can do some discovery for pcc
and set the ISA accordingly (either power8 or power9). If I
understand it correctly, power8 is a different architecture from
power9 (I could be wrong on this), so this is desirable. There's
some logic in config/ppc/meson.build, but it doesn't seem
sufficient as a discovery

mechanism between power8/power9.

quoted

POWER8 code (Power ISA v2.07) runs on POWER9 CPUs (Power ISA
v3.0), so setting cpu_instruction_set to GENERIC is a reasonable option.
POWER10 CPUs (Power ISA v3.1) are around the corner so I want to
make sure developers can tune the application for the platform
as easily as possible.  I'm fine with supporting GENERIC, just
need clear instructions on how to build for a particular ISA.

That's good to hear. Setting cpu_instruction_set will set the ISA.

We'll need to document the behavior properly, but I'm not sure where -

Bruce?

quoted

Seems like meson_options.txt doesn't have enough room for that.

quoted

Yes, agreed. I suggest putting in the option help text a link to the
documentation where we explain the options more fully.

/Bruce

You mentioned in the kni cross compile patch that we should do a separate

patch where we explain the option in docs and I believe this would go into that
patch. Before we do that, let's figure out the best description without the link. I
currently have:

quoted

option('cpu_instruction_set', type: 'string', value: 'auto',
	description: 'Set the target machine ISA (instruction set
architecture). Will be set according to the platform option by default.')

option('platform', type: 'string', value: 'generic',

quoted

	description: 'Platform to build, either "native" or "generic".')

What do you think? Should we expand the platform description a bit?

Are there not more platform options than just those two?

We're adding more in http://patches.dpdk.org/project/dpdk/patch/1612361037-12746-3-git-send-email-juraj.linkes@pantheon.tech/. I don't think there are more than two without that.

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