Re: [PATCH v2 3/5] riscv: Vector checksum header

From: Charlie Jenkins <charlie@rivosinc.com>
To: Conor Dooley <conor@kernel.org>
Cc: Albert Ou <aou@eecs.berkeley.edu>,
	linux-kernel@vger.kernel.org, Palmer Dabbelt <palmer@dabbelt.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	linux-riscv@lists.infradead.org
Subject: Re: [PATCH v2 3/5] riscv: Vector checksum header
Date: Thu, 7 Sep 2023 10:41:24 -0700	[thread overview]
Message-ID: <ZPoLRHq07Ttgf7rj@ghost> (raw)
In-Reply-To: <20230907-6ed9570259e770b6a472ee61@fedora>

On Thu, Sep 07, 2023 at 10:58:33AM +0100, Conor Dooley wrote:
> On Tue, Sep 05, 2023 at 09:46:52PM -0700, Charlie Jenkins wrote:
> > Vector code is written in assembly rather than using the GCC vector
> > instrinsics because they did not provide optimal code. Vector
> > instrinsic types are still used so the inline assembly can
> > appropriately select vector registers. However, this code cannot be
> > merged yet because it is currently not possible to use vector
> > instrinsics in the kernel because vector support needs to be directly
> > enabled by assembly.
> > 
> > Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
> > ---
> >  arch/riscv/include/asm/checksum.h | 87 +++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 87 insertions(+)
> > 
> > diff --git a/arch/riscv/include/asm/checksum.h b/arch/riscv/include/asm/checksum.h
> > index 3f9d5a202e95..1d6c23cd1221 100644
> > --- a/arch/riscv/include/asm/checksum.h
> > +++ b/arch/riscv/include/asm/checksum.h
> > @@ -10,6 +10,10 @@
> >  #include <linux/in6.h>
> >  #include <linux/uaccess.h>
> >  
> > +#ifdef CONFIG_RISCV_ISA_V
> > +#include <riscv_vector.h>
> > +#endif
> > +
> >  #ifdef CONFIG_32BIT
> >  typedef unsigned int csum_t;
> >  #else
> > @@ -43,6 +47,89 @@ static inline __sum16 csum_fold(__wsum sum)
> >   */
> >  static inline __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
> >  {
> > +#ifdef CONFIG_RISCV_ISA_V
> > +	if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
> > +		/*
> > +		 * Vector is likely available when the kernel is compiled with
> > +		 * vector support, so nop when vector is available and jump when
> > +		 * vector is not available.
> > +		 */
> > +		asm_volatile_goto(ALTERNATIVE("j %l[no_vector]", "nop", 0,
> > +					      RISCV_ISA_EXT_v, 1)
> > +				  :
> > +				  :
> > +				  :
> > +				  : no_vector);
> > +	} else {
> > +		if (!__riscv_isa_extension_available(NULL, RISCV_ISA_EXT_v))
> > +			goto no_vector;
> > +	}
> > +
> > +	vuint64m1_t prev_buffer;
> > +	vuint32m1_t curr_buffer;
> > +	unsigned int vl;
> > +#ifdef CONFIG_32_BIT
> > +	csum_t high_result, low_result;
> > +
> > +	riscv_v_enable();
> > +	asm(".option push						\n\
> > +	.option arch, +v						\n\
> > +	vsetivli x0, 1, e64, ta, ma					\n\
> 
> Also, I don't see that you have addressed previous review comments from
> Samuel:
> https://lore.kernel.org/linux-riscv/0a8c98bf-46da-e77a-0431-a6c1e224af2e@sifive.com/
I added the check for vector as Samuel suggested, but then I
accidentally used riscv_v_enable() instead of kernel_vector_begin(), I
will make that change.

- Charlie

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