From: Charlie Jenkins <charlie@rivosinc.com>
To: David Laight <David.Laight@aculab.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Conor Dooley <conor@kernel.org>,
Palmer Dabbelt <palmer@dabbelt.com>,
Paul Walmsley <paul.walmsley@sifive.com>,
"linux-riscv@lists.infradead.org"
<linux-riscv@lists.infradead.org>
Subject: Re: [PATCH v5 1/4] asm-generic: Improve csum_fold
Date: Fri, 15 Sep 2023 11:45:19 -0400 [thread overview]
Message-ID: <ZQR8DyY2wlHE1QHZ@ghost> (raw)
In-Reply-To: <b6bd38541255470b97bbaf3e6cdb4265@AcuMS.aculab.com>
On Fri, Sep 15, 2023 at 07:29:23AM +0000, David Laight wrote:
> From: Charlie Jenkins
> > Sent: 15 September 2023 04:50
> >
> > This csum_fold implementation introduced into arch/arc by Vineet Gupta
> > is better than the default implementation on at least arc, x86, arm, and
> > riscv. Using GCC trunk and compiling non-inlined version, this
> > implementation has 41.6667%, 25%, 16.6667% fewer instructions on
> > riscv64, x86-64, and arm64 respectively with -O3 optimization.
>
> Nit-picking the commit message...
> Some of those architectures have their own asm implementation.
> The arm one is better than the C code below, the x86 ones aren't.
I can clean up the commit message to be more accurate.
>
> I think that only sparc32 (carry flag but no rotate) and
> arm/arm64 (barrel shifter on every instruction) have versions
> that are better than the one here.
>
> Since I suggested it to Charlie:
>
> Reviewed-by: David Laight <david.laight@aculab.com>
>
> >
> > Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
> > ---
> > include/asm-generic/checksum.h | 5 +----
> > 1 file changed, 1 insertion(+), 4 deletions(-)
> >
> > diff --git a/include/asm-generic/checksum.h b/include/asm-generic/checksum.h
> > index 43e18db89c14..adab9ac4312c 100644
> > --- a/include/asm-generic/checksum.h
> > +++ b/include/asm-generic/checksum.h
> > @@ -30,10 +30,7 @@ extern __sum16 ip_fast_csum(const void *iph, unsigned int ihl);
> > */
> > static inline __sum16 csum_fold(__wsum csum)
> > {
> > - u32 sum = (__force u32)csum;
>
> You'll need to re-instate that line to stop sparse complaining.
I will add that back, thanks.
- Charlie
>
> > - sum = (sum & 0xffff) + (sum >> 16);
> > - sum = (sum & 0xffff) + (sum >> 16);
> > - return (__force __sum16)~sum;
> > + return (__force __sum16)((~csum - ror32(csum, 16)) >> 16);
> > }
> > #endif
> >
> >
> > --
> > 2.42.0
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
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next prev parent reply other threads:[~2023-09-15 15:45 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-15 3:49 [PATCH v5 0/4] riscv: Add fine-tuned checksum functions Charlie Jenkins
2023-09-15 3:49 ` [PATCH v5 1/4] asm-generic: Improve csum_fold Charlie Jenkins
2023-09-15 7:29 ` David Laight
2023-09-15 15:45 ` Charlie Jenkins [this message]
2023-09-15 3:49 ` [PATCH v5 2/4] riscv: Checksum header Charlie Jenkins
2023-09-15 10:07 ` Emil Renner Berthing
2023-09-15 15:25 ` Charlie Jenkins
2023-09-15 3:49 ` [PATCH v5 3/4] riscv: Add checksum library Charlie Jenkins
2023-09-15 3:49 ` [PATCH v5 4/4] riscv: Test checksum functions Charlie Jenkins
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