On Wed, Mar 10, 2021 at 1:12 PM Juraj Linkeš [off-list ref] wrote:

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-----Original Message-----
From: Honnappa Nagarahalli <redacted>
Sent: Tuesday, March 9, 2021 8:55 PM
To: Juraj Linkeš <redacted>; Jerin Jacob
[off-list ref]
Cc: Bruce Richardson <redacted>; Ruifeng Wang
[off-list ref]; vcchunga@amazon.com; Dharmik Thakkar
[off-list ref]; hemant.agrawal@nxp.com; Ajit Khaparde
(ajit.khaparde@broadcom.com) [off-list ref];
ferruh.yigit@intel.com; aboyer@pensando.io; lironh@marvell.com;
dev@dpdk.org; nd [off-list ref]; nd [off-list ref]
Subject: RE: [PATCH v16 1/3] build: disable/enable drivers in Arm builds

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On Tue, Mar 09, 2021 at 08:58:39AM +0000, Juraj Linkeš wrote:

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Honnappa, Thomas, Bruce, Jerin, you've comments in the past.
Do you have

any further input?

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I think we just need to agree on the allowlist/blocklist
mechanism. The current

commit allows specifying either an allowlist or a
blocklist, but not

both.

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However, it would possible to implement specifying both -
first we'll allow what's in allowlist and then we'll
remove from that set what's

in blocklist.

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Thoughts?

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If we have both, I think limiting to only one is by far
the sanest

option.

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+1

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I'm not fully convinced by the need to have both, since
the blocklist allows wildcarding and exception cases. For
example "net/[!i]*" will blocklist all net drivers except
those starting with an "i". Admittedly, for usability
purposes having an allowlist might

work better.

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If we only want to build a handful of drivers then the list
could be very long

(which was the original reason behind having an allowlist),
such as

here:

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https://gerrit.fd.io/r/gitweb?p=vpp.git;a=blob;f=build/exter
na
l/
pa
ck ag

es/dpdk.mk;h=c35ac84c27b19411a0cfdf9a3524fdf36024762c;hb=HEAD

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An allowlist could also help with maintenance - users won't
need to add

new drivers to their blocklists (if that's what users need,
like in the case of VPP).

+1 for allowlist.

May be I am missing something here. By creating an allowlist,
does it mean drivers are disabled (from compilation) by default?
For a server platform, where almost all the drivers can be
compiled, does the allowlist

contain all the drivers?

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If no allowlist is specified, then everythin will be built -
nothing will be filtered.

That's confusing.
If a platform like bluefield has an allow list, a new PMD that gets
added will not be compiled for that platform unless someone
explicitly adds

it to the allow list.

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Is my understanding correct?

Yes.

With this it becomes very easy to skip compiling on a platform.

It wouldn't be mandatory. Maybe I should've said we would be able to choose between three behaviors - the current (where everything is built), with allowlist or with blocklist.

But maybe the worry is that someone will use the allowlist without fully understanding the consequences?

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Whereas if the bluefield platform had a block list, then the new PMD
would be compiled for bluefield platform.

Again, yes.

Supporting both would give us the option to choose between the two
behaviors.

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If we assume by default everything should compile on Arm
platform, but allow for few exceptions (where things are really
painful to fix, for
ex: compiler needs to be fixed), having a blocklist should be

shorter/better?

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The blocklist is, I think, agreed upon by everyone. The question
is whether we want to support the allowlist alongside it and there
seem to be enough reasons to do that.

Sorry, may be this is answered already, but, what additional benefit
does allowlist provide over the blocklist?

VPP could use it:
https://gerrit.fd.io/r/gitweb?p=vpp.git;a=blob;f=build/external/packag
es/dpdk .mk;h=c35ac84c27b19411a0cfdf9a3524fdf36024762c;hb=HEAD

They're disabling almost everything so an allowlist would fit there.
And they won't need to update the list when a new driver is added
(which they won't need).

This is different from how we started this discussion. The current discussion was
for DPDK internal use. But the one you are referencing above is for users of
DPDK. I am fine for providing the allow list for the users of DPDK. But for DPDK
internal, I think block list is enough.

That's an interesting suggestion. Jerin, what do you think? Why did you want to have an allowlist? Would this work?

# The very reason why VPP chooses to have allow list so that they can
control what needs to include.
# Another use case is like, in SoCs have fixed internal devices, we
can have optimized build for that can have only allow list
of the drivers that care about
# For server market, block list makes sense
# For embedded SoC, allow list makes sense.
# Ideal situation is if we support both.
# I dont quite understand the above comments for internal use vs
external use. If it is exposed
as a meson option then I think, it does not matter. Right?

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I think it was Jerin who suggested the allowlist. I don't know of an
Arm usecase for it, but maybe he has an example.

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By having an allowlist, we will end up with a large part of the
code that might not compile on Arm platforms.

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One final thought, if we add a driver allowlist for cross
files, should we also add one as a top-level meson option
also for

consistency?

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This definitely makese sense. I was thinking about this and
wasn't sure

whether I should put it into this commit or a separate one.
The commit evolved a bit and now that it's just an
implementation of an allow/blocklist it makes sense to include
a meson option in it I think
- I'll put it into the next version.

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/Bruce