linux-kernel - Re: [PATCH v4 4/5] riscv: Vector checksum library

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Date:   Thu, 14 Sep 2023 13:29:18 -0400
From:   Charlie Jenkins <charlie@...osinc.com>
To:     Conor Dooley <conor@...nel.org>
Cc:     Conor Dooley <conor.dooley@...rochip.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Samuel Holland <samuel.holland@...ive.com>,
        David Laight <David.Laight@...lab.com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>
Subject: Re: [PATCH v4 4/5] riscv: Vector checksum library

On Thu, Sep 14, 2023 at 05:29:29PM +0100, Conor Dooley wrote:
> On Thu, Sep 14, 2023 at 12:14:16PM -0400, Charlie Jenkins wrote:
> > On Thu, Sep 14, 2023 at 01:46:29PM +0100, Conor Dooley wrote:
> > > On Mon, Sep 11, 2023 at 03:57:14PM -0700, Charlie Jenkins wrote:
> > > > This patch is not ready for merge as vector support in the kernel is
> > > > limited. However, the code has been tested in QEMU so the algorithms
> > > > do work. This code requires the kernel to be compiled with C vector
> > > > support, but that is not yet possible. It is written in assembly
> > > > rather than using the GCC vector instrinsics because they did not
> > > > provide optimal code.
> > > > 
> > > > Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
> > > > ---
> > > >  arch/riscv/lib/csum.c | 92 +++++++++++++++++++++++++++++++++++++++++++++++++++
> > > >  1 file changed, 92 insertions(+)
> > > > 
> > > > diff --git a/arch/riscv/lib/csum.c b/arch/riscv/lib/csum.c
> > > > index 47d98c51bab2..eb4596fc7f5b 100644
> > > > --- a/arch/riscv/lib/csum.c
> > > > +++ b/arch/riscv/lib/csum.c
> > > > @@ -12,6 +12,10 @@
> > > >  
> > > >  #include <net/checksum.h>
> > > >  
> > > > +#ifdef CONFIG_RISCV_ISA_V
> > > > +#include <riscv_vector.h>
> > > 
> > > What actually includes this header, I don't see it in either Andy's
> > > in-kernel vector series or Bjorn's blake2 one.
> > > Can you link to the pre-requisites in your cover letter please.
> > > 
> > > Thanks,
> > > Conor.
> > 
> > It is defined here:
> > https://github.com/riscv-non-isa/rvv-intrinsic-doc/blob/main/doc/rvv-intrinsic-spec.adoc.
> > The header is for the vector intrinsics that are supported by llvm and
> > gcc.
> 
> Well, whatever you're doing with it does not work, producing 3600 or so
> fatal errors during compilation, all saying:
> ../arch/riscv/include/asm/checksum.h:14:10: fatal error: riscv_vector.h: No such file or directory
> 
> Do you have some makefile hack somewhere that's not part of this
> patchset? Also, I'm dumb, but can you show me where are the actual
> intrinsics are being used in this patch anyway? I just seem some
> types & asm.
> 
> Thanks,
> Conor.
> 

Intrinsics are needed for the vector types. Vector types are needed to
get the inline asm to select vector registers at compile time. I could
manually select vector registers to use but that is not ideal. In order
to get this to work, vector has to be enabled in the compiler. This
patch will not compile right now, but since people are working on vector
I was hoping that it would be possible in the future. Palmer recommended
that I just put up this patch for now since I had the code, but only the
non-vector versions should be candidates for release for now.

- Charlie