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

[Jerin Jacob <jerinjacobk@gmail.com>]

On Mon, 7 Oct, 2019, 11:35 PM Thomas Monjalon, <thomas@monjalon.net> wrote:

> 07/10/2019 15:00, Jerin Jacob:
> > On Mon, 7 Oct, 2019, 6:03 PM Thomas Monjalon wrote:
> > > 04/10/2019 17:39, Jerin Jacob:
> > > > On Thu, Oct 3, 2019 at 8:35 PM Ananyev, Konstantin wrote:
> > > > > > On Thu, Oct 3, 2019 at 6:21 PM Thomas Monjalon 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 am not against discussing the technical data about the 'patch' and
> review
> > it. If there is a review with respect to content of the patch it is very
> > good, I am happy to address it. Stuff like I don't have any control (
> > changing the licence) etc, I have am not comfortable to take  in last
> > minute. I have already shared the eBPF ARM64 JIT support in roadmap a
> month
> > ago before implementing it. No question asked that time. Spend a almost
> > month to add support for it and It is not a simple C code. Now I am not
> > comfortable in asking the fundamental questions like why this eBPF it
> self
> > is required and code duplication  ( code was duplicated when x86 support
> > has been added) and therefore stall the patch at this point of time,
> where
> > this library and x86 support added a year back.
>
> I really don't like this reaction.
>

If it hurts you in some way then I am sorry about that.

First, I never said this discussion was blocking the patch.
>

You said you have concern with this patch. Sorry,
I am not sure how to interpret that and if I don't jump in it will be
stalled for sure. That's my experience. Sorry if you dis agree.


Second, why am I the only one asking such obvious questions
> as not duplicating work?
>

Some things it does not converge at all. Especially relicecing some code
from linux. There are a lot developers(even me) are involved in that code
base. Why would everyone agree? The list would include a recent RISCV JIT
contributer from gmail.com as example.

Duplication the semantics some times gives the morecontrol. We already did
that for rte_flow, rcu etc. I have mentioned the performance reason as well
for JIT in the other thread.



>
> > > 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).
>
> You Jerin and Konstantin should have answered these questions
> a long time ago before starting such development.
> Is it so hard to require a bit of thoughts before starting something new?
>

For me, I don't see any better approach to have user space eBPF to support
all OS in DPDK.


> > Konstantin added enough data on ml this when this library gets added on
> > reply to different users.
>
> Really? which data?
>

I am talking about the discussion with
niterome developer.I don't have exact email thread, probably Konstantin may
have


>
> > > About your urge of having this code merged,
> > > please can you explain what is your usage?
> >
> > As an ARM64 maintainter, I would  like to fix any disparity in terms of
> the
> > features with respect to x86 and I have been doing for last 3 years. If
> > some one using eBPF on x86, I want to make sure it run in similar
> > "performance" on arm64 on architecture perspective.
>
> So we are debating about a library which is probably not used by anybody.
> That's not how I plan to spend my time on DPDK.
>

How do anyone know that the library is not used by anyone in community if
it is part of dpdk.org and a customer asked does arm64 has JIT support too.

If something needs to be dynamically controlled then eBPF can be used,
couple of use cases

# packet filtering
# debugging
# function call tracing
# There are some Lua JIT based dataplane implementations. Which can be
replaced with eBPF with JIT.




>
>
> Sorry Jerin, I really like working with you,
>

Mee too.

but I think you forward too much pressure here,
> instead of quietly discussing the future of DPDK.
>
> Please forget the deadline (we will agree on merging anyway)
>

Ok.

and let's restart from the beginning by answering simple questions:
> - what are the use cases of BPF in DPDK?
>

I meantioned what I know,

- how much we'll benefit from sharing code with Linux?
>

I have mentioned some of the performance constraint in the other thread.
Moreover I don't believe it is not easy task for Linux eBPF to run as
userspace and I not sure who is going to do that

- what can we lose in a single JIT implementation?
>

Sorry, I didn't understood this question?




>
>