linux-kernel - Re: [RFC PATCH bpf-next 0/3] bpf, riscv: Add compressed instructions to rv64 JIT

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Message-ID: <CAB-e3NQFE9rsVZ55Y=jivuBsd1A+V4GWtceqjOz80qtmFsFQVA@mail.gmail.com>
Date:   Wed, 15 Jul 2020 13:08:43 -0700
From:   Luke Nelson <luke.r.nels@...il.com>
To:     Björn Töpel <bjorn.topel@...il.com>
Cc:     Luke Nelson <lukenels@...washington.edu>,
        bpf <bpf@...r.kernel.org>, Xi Wang <xi.wang@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Netdev <netdev@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH bpf-next 0/3] bpf, riscv: Add compressed instructions
 to rv64 JIT

>
> First of all; Really nice work. I like this, and it makes the code
> easier to read as well (e.g. emit_mv). I'm a bit curious why you only
> did it for RV64, and not RV32? I have some minor comments on the
> patches. I strongly encourage you to submit this as a proper (non-RFC)
> set for bpf-next.
>

Thanks for the feedback! I'll clean up the patches and address your
comments in the next revision.

The patch adding RVC to the RV32 JIT is forthcoming; some of the
optimizations there are more difficult since the RV32 JIT makes more
use of "internal" jumps whose offsets depend on the sizes of emitted
instructions. I plan to clean up that code and add RVC support in a
future series.

- Luke