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

[Jerin Jacob <jerinjacobk@gmail.com>]

On Mon, 7 Oct, 2019, 6:03 PM Thomas Monjalon, <thomas@monjalon.net> wrote:

> 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 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 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).
>

Konstantin added enough data on ml this when this library gets added on
reply to different users.


> 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.



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