Re: [Qemu-devel] RISC-V: Vector && DSP Extension

From: Aleksandar Markovic <aleksandar.m.mail@gmail.com>
To: Chih-Min Chao <chihmin.chao@sifive.com>
Cc: Peter Maydell <peter.maydell@linaro.org>,
	"open list:RISC-V" <qemu-riscv@nongnu.org>,
	Sagar Karandikar <sagark@eecs.berkeley.edu>,
	bastian@mail.uni-paderborn.de, Palmer Dabbelt <palmer@sifive.com>,
	QEMU Developers <qemu-devel@nongnu.org>,
	Alistair Francis <Alistair.Francis@wdc.com>,
	liuzhiwei <zhiwei_liu@c-sky.com>
Subject: Re: [Qemu-devel] RISC-V: Vector && DSP Extension
Date: Thu, 8 Aug 2019 16:19:22 +0200	[thread overview]
Message-ID: <CAL1e-=iKYyWRkrOgEQ0ji67W1cfYc6iH-fPsF1wpYS84M46NNw@mail.gmail.com> (raw)
In-Reply-To: <CAEiOBXVDg-oaqWDpzFrsPjzt8jdmLt7DskG4=zXwYVUb+5=tfg@mail.gmail.com>

On Thu, Aug 8, 2019 at 3:48 PM Chih-Min Chao <chihmin.chao@sifive.com>
wrote:

>
>
> On Thu, Aug 8, 2019 at 7:29 PM Aleksandar Markovic <
> aleksandar.m.mail@gmail.com> wrote:
>
>> On Thu, Aug 8, 2019 at 11:52 AM liuzhiwei <zhiwei_liu@c-sky.com> wrote:
>>
>> > Hi all,
>> >
>> >     My workmate  and I have been working on Vector & Dsp extension, and
>> > I'd like to share develop status  with folks.
>> >
>> >     The spec references for  Vector extension is riscv-v-spec-0.7.1, and
>> > riscv-p-spec-0.5 for DSP extension.
>>
>>
>> Hello, Liu.
>>
>> I will not answer your questions directly, however I want to bring to you
>> and others another perspective on this situation.
>>
>> First, please provide the link to the specifications. Via Google, I found
>> that "riscv-v-spec-0.7.1" is titled "Working draft of the proposed RISC-V
>> V
>> vector extension". I could not find "riscv-p-spec-0.5".
>>
>> I am not sure what the QEMU policy towards "working draft proposal" type
>> of
>> specification is. Peter, can you perhaps clarify that or any other related
>> issue?
>>
>
> Hi Aleksandar,
>
> As for riscv-v-spec 0.7.1, it is first stable spec for target software
> development
> though the name is working draft.
>

Hello, Chih-Min.

Too many unclear points here.

What does this sentence mean? What is "stable"? Is that the same as
"final"? If the document is stable, why the title "draft/proposal"? Can a
"draft" be stable? Can you, or anybody else, guarantee that the final
version of this document will not affect QEMU implementation, if it is done
by the current document? If not, why would you like QEMU upstream to
support something not fully specified? Why has the final document not been
released, if the situation is stable?.....

Yours,
Aleksandar

  The architecture skeleton is fix and most of
> work are focusing the issues related to micro-architecture implementation
> complexity.
> Sifive has released an open source implementation on spike simulation and
> Imperas also
> provides another implementation with its binary simulator.  I think it is
> worth to include the extension
> in Qemu at this moment.
>
> As for riscv-p-spec-0.5, I think Andes has fully supported this extension
> and should release more
> detailed spec in the near future (described Riscv Technical Update
> 2019/06).
> They have implement lots of DSP kernel based on this extension and also
> provided impressed
> performance result.  It is also worth to be reviewed (at least [RFC]) if
> the detailed  spec is public.
>
>
> ref:
>      1.
> https://content.riscv.org/wp-content/uploads/2019/06/17.40-Vector_RISCV-20190611-Vectors.pdf
>      2.
> https://content.riscv.org/wp-content/uploads/2019/06/17.20-P-ext-RVW-Zurich-20190611.pdf
>      3.
> https://content.riscv.org/wp-content/uploads/2019/06/10.05-TechCommitteeUpdate-June-2019-Copy.pdf
>
>
> chihmin
>
>
> I would advice some caution in these cases. The major issue is backward
>> compatibility, but there are other issues too. Let's say, fairness. If we
>> let emulation of a component based on a "working draft proposal" be
>> integrated into QEMU, this will set a precedent, and many other developer
>> would rightfully ask for their contributions based on drafts to be
>> integrated into QEMU. Our policy should be as equal as possible to all
>> contribution, large or small, riscv or alpha, cpu or device, tcg or kvm -
>> in my honest opinion. QEMU upstream should not be a collecting place for
>> all imaginable experimentations, certain criteria on what is appropriate
>> for upstreaming exist and must continue to exist.
>>
>> Yours,
>> Aleksandar
>>
>>
>>
>>
>> > The code of vector extension is
>> > ready and under testing,  the first patch will be sent about two weeks
>> > later. After that we will forward working on DSP extension, and send the
>> > first patch in middle  October.
>> >
>> >      Could the maintainers  tell me whether the specs referenced are
>> > appropriate? Is anyone working on these extensions?  I'd like to get
>> > your status, and maybe discuss questions and work togather.
>> >
>> > Best Regards
>> >
>> > LIU Zhiwei
>> >
>> >
>> >
>> >
>>
>