netdev - [PATCH] x86/lib: Remove the special case for odd-aligned buffers in csum

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Message-ID: <45d12aa0c95049a392d52ff239d42d83@AcuMS.aculab.com>
Date:   Mon, 13 Dec 2021 14:43:48 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     David Laight <David.Laight@...LAB.COM>,
        'Noah Goldstein' <goldstein.w.n@...il.com>,
        Eric Dumazet <edumazet@...gle.com>
CC:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        X86 ML <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "alexanderduyck@...com" <alexanderduyck@...com>,
        open list <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>
Subject: [PATCH] x86/lib: Remove the special case for odd-aligned buffers in
 csum_partial.c

There is no need to special case the very unusual odd-aligned buffers.
They are no worse than 4n+2 aligned buffers.

Signed-off-by: David Laight <david.laight@...lab.com>
---

On an i7-7700 misaligned buffers add 2 or 3 clocks (in 115) to a 512 byte
  checksum.
That is just measuring the main loop with an lfence prior to rdpmc to
read PERF_COUNT_HW_CPU_CYCLES.

 arch/x86/lib/csum-partial_64.c | 16 +---------------
 1 file changed, 1 insertion(+), 15 deletions(-)

diff --git a/arch/x86/lib/csum-partial_64.c b/arch/x86/lib/csum-partial_64.c
index 40b527ba1da1..abf819dd8525 100644
--- a/arch/x86/lib/csum-partial_64.c
+++ b/arch/x86/lib/csum-partial_64.c
@@ -35,17 +35,7 @@ static inline unsigned short from32to16(unsigned a)
 __wsum csum_partial(const void *buff, int len, __wsum sum)
 {
 	u64 temp64 = (__force u64)sum;
-	unsigned odd, result;
-
-	odd = 1 & (unsigned long) buff;
-	if (unlikely(odd)) {
-		if (unlikely(len == 0))
-			return sum;
-		temp64 = ror32((__force u32)sum, 8);
-		temp64 += (*(unsigned char *)buff << 8);
-		len--;
-		buff++;
-	}
+	unsigned result;
 
 	while (unlikely(len >= 64)) {
 		asm("addq 0*8(%[src]),%[res]\n\t"
@@ -130,10 +120,6 @@ __wsum csum_partial(const void *buff, int len, __wsum sum)
 #endif
 	}
 	result = add32_with_carry(temp64 >> 32, temp64 & 0xffffffff);
-	if (unlikely(odd)) { 
-		result = from32to16(result);
-		result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
-	}
 	return (__force __wsum)result;
 }
 EXPORT_SYMBOL(csum_partial);
-- 
2.17.1

-
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