* [PATCH] powerpc: Reduce csum_add() complexity for PPC64
@ 2022-02-12 7:36 Christophe Leroy
2022-05-15 10:28 ` Michael Ellerman
0 siblings, 1 reply; 2+ messages in thread
From: Christophe Leroy @ 2022-02-12 7:36 UTC (permalink / raw)
To: Benjamin Herrenschmidt, Paul Mackerras, Michael Ellerman
Cc: Christophe Leroy, linux-kernel, linuxppc-dev
PPC64 does everything in C, gcc is able to skip calculation
when one of the operands in zero.
Move the constant folding in PPC32 part.
This helps GCC and reduces ppc64_defconfig by 170 bytes.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
arch/powerpc/include/asm/checksum.h | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)
diff --git a/arch/powerpc/include/asm/checksum.h b/arch/powerpc/include/asm/checksum.h
index 3288a1bf5e8d..e4e25b46ac49 100644
--- a/arch/powerpc/include/asm/checksum.h
+++ b/arch/powerpc/include/asm/checksum.h
@@ -95,16 +95,15 @@ static __always_inline __wsum csum_add(__wsum csum, __wsum addend)
{
#ifdef __powerpc64__
u64 res = (__force u64)csum;
-#endif
+
+ res += (__force u64)addend;
+ return (__force __wsum)((u32)res + (res >> 32));
+#else
if (__builtin_constant_p(csum) && csum == 0)
return addend;
if (__builtin_constant_p(addend) && addend == 0)
return csum;
-#ifdef __powerpc64__
- res += (__force u64)addend;
- return (__force __wsum)((u32)res + (res >> 32));
-#else
asm("addc %0,%0,%1;"
"addze %0,%0;"
: "+r" (csum) : "r" (addend) : "xer");
--
2.34.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] powerpc: Reduce csum_add() complexity for PPC64
2022-02-12 7:36 [PATCH] powerpc: Reduce csum_add() complexity for PPC64 Christophe Leroy
@ 2022-05-15 10:28 ` Michael Ellerman
0 siblings, 0 replies; 2+ messages in thread
From: Michael Ellerman @ 2022-05-15 10:28 UTC (permalink / raw)
To: Christophe Leroy, Michael Ellerman, Paul Mackerras,
Benjamin Herrenschmidt
Cc: linuxppc-dev, linux-kernel
On Sat, 12 Feb 2022 08:36:17 +0100, Christophe Leroy wrote:
> PPC64 does everything in C, gcc is able to skip calculation
> when one of the operands in zero.
>
> Move the constant folding in PPC32 part.
>
> This helps GCC and reduces ppc64_defconfig by 170 bytes.
>
> [...]
Applied to powerpc/next.
[1/1] powerpc: Reduce csum_add() complexity for PPC64
https://git.kernel.org/powerpc/c/f206fdd9d41bf7deb96219b8ca3499a5abd79b83
cheers
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