Re: [dpdk-dev] [PATCH 0/8] eBPF arm64 JIT support

From: Thomas Monjalon <thomas@monjalon.net>
To: Jerin Jacob <jerinjacobk@gmail.com>
Cc: "Ananyev, Konstantin" <konstantin.ananyev@intel.com>,
	Jerin Jacob <jerinj@marvell.com>, dpdk-dev <dev@dpdk.org>,
	Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>,
	Gavin Hu <gavin.hu@arm.com>
Subject: Re: [dpdk-dev] [PATCH 0/8] eBPF arm64 JIT support
Date: Mon, 07 Oct 2019 14:33:32 +0200	[thread overview]
Message-ID: <4310069.WdzTAdBlsv@xps> (raw)
In-Reply-To: <CALBAE1M+Wki7MB2EVq5zeW+c_aXMunRnYxZrm3BSQjdoP9CTyQ@mail.gmail.com>

04/10/2019 17:39, Jerin Jacob:
> On Thu, Oct 3, 2019 at 8:35 PM Ananyev, Konstantin
> <konstantin.ananyev@intel.com> wrote:
> >
> > Hi everyone,
> >
> > >
> > > On Thu, Oct 3, 2019 at 6:21 PM Thomas Monjalon <thomas@monjalon.net> wrote:
> > > >
> > > > 03/09/2019 12:59, jerinj@marvell.com:
> > > > > Added eBPF arm64 JIT support to improve the eBPF program performance
> > > > > on arm64.
> > > > >
> > > > >  lib/librte_bpf/bpf_jit_arm64.c         | 1451 ++++++++++++++++++++++++
> > > >
> > > > I am concerned about duplicating the BPF JIT effort in DPDK and Linux.
> > > > Could we try to pull the Linux JIT?
> > > > Is the license the only issue?
> > >
> > > That's one issue.
> > >
> > > >
> > > > After a quick discussion, it seems the Linux authors are OK to arrange
> > > > their JIT code for sharing with userspace projects.
> > >
> > > I did a clean room implementation considering some optimization for
> > > DPDK etc(Like if stack is not used then don't push stack etc)
> > > and wherever Linux can be improved, I have submitted the patch also to
> > > Linux as well.(Some more pending as well)
> > >
> > > https://github.com/torvalds/linux/commit/504792e07a44844f24e9d79913e4a2f8373cd332
> > >
> > > And Linux has a framework for instruction generation for debugging
> > > etc. So We can not copy and paste the code
> > > from Linux as is.
> > >
> > > My view to keep a different code base optimize for DPDK use cases and
> > > library requirements(for example, tail call is not supported in DPDK).
> > > For arm64/x86 case the code is done so it is not worth sync with
> > > Linux. For new architecture, it can be if possible.
> > >
> > > Konstantin,
> > > Your thoughts?
> > >
> >
> > My thought would be that if we have JIT eBPF compiler already in DPDK
> > for one arch (x86) there is absolutely no reason why we shouldn't allow it for different arch (arm).
> > About having a common code-base with Linux eBPF JITs implementation -
> > I think it is a very good idea,
> > but I don’t' think it could be achieved without significant effort.
> > DPDK and Linux JIT code-generators differ quite a bit.
> > So my suggestion - let's go ahead and integrate Jerin patch into 19.11,
> > meanwhile start talking with linux guys how common JIT code-base could be achieved.
> 
> I agree with Konstantin here.
> 
> Thomas,
> 
> Just confirm the following:
> 
> While we continue to have 'advanced' discussion on avoiding code duplication etc
> and it will take a couple of months to converge(if at all it happens)
> 
> Just to be clear, I assume, you are OK to merge this code for 19.11(If
> no more technical comment on the patch).
> 
> I am only afraid of, our typical last-minute surprise pattern and
> followed by back and forth open ended discussions.
> 
> i.e
> 
> # Code submitted before the proposal window
> # Gets ACK from Maintainer
> # New non-technical concerns start just before RC1

I hope you are not against discussing the real good questions,
even if they come a month after the first submission.

I don't care merging such patch in 19.11,
but I would have preferred such questions were open
when introducing this new library (for x86).

About your urge of having this code merged,
please can you explain what is your usage?