| Message ID | 20230914-optimize_checksum-v5-1-c95b82a2757e@rivosinc.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | riscv: Add fine-tuned checksum functions | expand |
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 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. > - 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)
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)
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; - sum = (sum & 0xffff) + (sum >> 16); - sum = (sum & 0xffff) + (sum >> 16); - return (__force __sum16)~sum; + return (__force __sum16)((~csum - ror32(csum, 16)) >> 16); } #endif
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. Signed-off-by: Charlie Jenkins <charlie@rivosinc.com> --- include/asm-generic/checksum.h | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-)