Implement assembly routine for csum_partial for 64 bit x86. This
primarily speeds up checksum calculation for smaller lengths such as
those that are present when doing skb_postpull_rcsum when getting
CHECKSUM_COMPLETE from device or after CHECKSUM_UNNECESSARY
conversion.
This implementation is similar to csum_partial implemented in
checksum_32.S, however since we are dealing with 8 bytes at a time
there are more cases for small lengths-- for that we employ a jump
table. Also, we don't do anything special for alignment, unaligned
accesses on x86 do not appear to be a performance issue.
Testing:
Verified correctness by testing arbitrary length buffer filled with
random data. For each buffer I compared the computed checksum
using the original algorithm for each possible alignment (0-7 bytes).
Checksum performance:
Isolating old and new implementation for some common cases:
Old New
Case nsecs nsecs Improvement
---------------------+--------+--------+-----------------------------
1400 bytes (0 align) 194.5 174.3 10% (Big packet)
40 bytes (0 align) 13.8 5.8 57% (Ipv6 hdr common case)
8 bytes (4 align) 8.4 2.9 65% (UDP, VXLAN in IPv4)
14 bytes (0 align) 10.6 5.8 45% (Eth hdr)
14 bytes (4 align) 10.8 5.8 46% (Eth hdr in IPv4)
Signed-off-by: Tom Herbert <t...@herbertland.com>
---
arch/x86/include/asm/checksum_64.h | 5 ++
arch/x86/lib/csum-partial_64.S | 147 ++++++++++++++++++++++++++++++++++++
arch/x86/lib/csum-partial_64.c | 148 -------------------------------------
3 files changed, 152 insertions(+), 148 deletions(-)
create mode 100644 arch/x86/lib/csum-partial_64.S
delete mode 100644 arch/x86/lib/csum-partial_64.c
diff --git a/arch/x86/include/asm/checksum_64.h
b/arch/x86/include/asm/checksum_64.h
index cd00e17..a888f65 100644
--- a/arch/x86/include/asm/checksum_64.h
+++ b/arch/x86/include/asm/checksum_64.h
@@ -128,6 +128,11 @@ static inline __sum16 csum_tcpudp_magic(__be32 saddr,
__be32 daddr,
*/
extern __wsum csum_partial(const void *buff, int len, __wsum sum);
+static inline __sum16 ip_compute_csum(const void *buff, int len)
+{
+ return csum_fold(csum_partial(buff, len, 0));
+}
+
#define _HAVE_ARCH_COPY_AND_CSUM_FROM_USER 1
#define HAVE_CSUM_COPY_USER 1
diff --git a/arch/x86/lib/csum-partial_64.S b/arch/x86/lib/csum-partial_64.S
new file mode 100644
index 0000000..8e387bb
--- /dev/null
+++ b/arch/x86/lib/csum-partial_64.S
@@ -0,0 +1,147 @@
+/* Copyright 2016 Tom Herbert <t...@herbertland.com>
+ *
+ * Checksum partial calculation
+ *
+ * __wsum csum_partial(const void *buff, int len, __wsum sum)
+ *
+ * Computes the checksum of a memory block at buff, length len,
+ * and adds in "sum" (32-bit)
+ *
+ * Returns a 32-bit number suitable for feeding into itself
+ * or csum_tcpudp_magic
+ *
+ * Register usage:
+ * %rdi: argument 1, buff
+ * %rsi: argument 2, length
+ * %rdx: argument 3, add in value
+ * %rax,%eax: accumulator and return value
+ * %rcx,%ecx: counter and tmp
+ * %r11: tmp
+ *
+ * Basic algorithm:
+ * 1) Sum 8 bytes at a time using adcq (unroll main loop
+ * to do 64 bytes at a time)
+ * 2) Sum remaining length (less than 8 bytes)
+ *
+ * Note that buffer aligment is not considered, unaligned accesses on x86 don't
+ * seem to be a performance hit (CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS is
set).
+ */
+
+#include <linux/linkage.h>
+#include <asm/errno.h>
+#include <asm/asm.h>
+
+#define branch_tbl_len .L_branch_tbl_len
+
+ENTRY(csum_partial)
+ movl %edx, %eax /* Initialize with initial sum argument */
+
+ /* Check length */
+ cmpl $8, %esi
+ jg 10f
+ jl 20f
+
+ /* Exactly 8 bytes length */
+ addl (%rdi), %eax
+ adcl 4(%rdi), %eax
+ adcl $0, %eax
+ ret
+
+ /* Less than 8 bytes length */
+20: clc
+ jmpq *branch_tbl_len(, %rsi, 8)
+
+ /* Greater than 8 bytes length. Determine number of quads (n). Sum
+ * over first n % 8 quads
+ */
+10: movl %esi, %ecx
+ shrl $3, %ecx
+ andl $0x7, %ecx
+ negq %rcx
+ lea 20f(, %rcx, 4), %r11
+ clc
+ jmp *%r11
+
+.align 8
+ adcq 6*8(%rdi),%rax
+ adcq 5*8(%rdi),%rax
+ adcq 4*8(%rdi),%rax
+ adcq 3*8(%rdi),%rax
+ adcq 2*8(%rdi),%rax
+ adcq 1*8(%rdi),%rax
+ adcq 0*8(%rdi),%rax
+ nop
+20: /* #quads % 8 jump table base */
+
+ adcq $0, %rax
+ shlq $3, %rcx
+ subq %rcx, %rdi /* %rcx is already negative length */
+
+ /* Now determine number of blocks of 8 quads. Sum 64 bytes at a time
+ * using unrolled loop.
+ */
+ movl %esi, %ecx
+ shrl $6, %ecx
+ jz 30f
+ clc
+
+ /* Main loop */
+40: adcq 0*8(%rdi),%rax
+ adcq 1*8(%rdi),%rax
+ adcq 2*8(%rdi),%rax
+ adcq 3*8(%rdi),%rax
+ adcq 4*8(%rdi),%rax
+ adcq 5*8(%rdi),%rax
+ adcq 6*8(%rdi),%rax
+ adcq 7*8(%rdi),%rax
+ lea 64(%rdi), %rdi
+ loop 40b
+
+ adcq $0, %rax
+
+ /* Handle remaining length which is < 8 bytes */
+30: andl $0x7, %esi
+
+ /* Fold 64 bit sum to 32 bits */
+ movq %rax, %rcx
+ shrq $32, %rcx
+ addl %ecx, %eax
+
+ jmpq *branch_tbl_len(, %rsi, 8)
+
+/* Length table targets */
+
+107: /* Length 7 */
+ adcw 4(%rdi), %ax
+105: /* Length 5 */
+ adcw 2(%rdi), %ax
+103: /* Length 3 */
+ adcw (%rdi), %ax
+101: /* Length 1, grab the odd byte */
+ adcb -1(%rdi, %rsi), %al
+ adcb $0, %ah
+ adcl $0, %eax
+ ret
+106: /* Length 6 */
+ adcw 4(%rdi), %ax
+104: /* Length 4 */
+ adcl (%rdi), %eax
+ adcl $0, %eax
+ ret
+102: /* Length 2 */
+ adcw (%rdi), %ax
+100: /* Length 0 */
+ adcl $0, %eax
+ ret
+
+.section .rodata
+.align 64
+.L_branch_tbl_len:
+ .quad 100b
+ .quad 101b
+ .quad 102b
+ .quad 103b
+ .quad 104b
+ .quad 105b
+ .quad 106b
+ .quad 107b
diff --git a/arch/x86/lib/csum-partial_64.c b/arch/x86/lib/csum-partial_64.c
deleted file mode 100644
index 9845371..0000000
--- a/arch/x86/lib/csum-partial_64.c
+++ /dev/null
@@ -1,148 +0,0 @@
-/*
- * arch/x86_64/lib/csum-partial.c
- *
- * This file contains network checksum routines that are better done
- * in an architecture-specific manner due to speed.
- */
-
-#include <linux/compiler.h>
-#include <linux/module.h>
-#include <asm/checksum.h>
-
-static inline unsigned short from32to16(unsigned a)
-{
- unsigned short b = a >> 16;
- asm("addw %w2,%w0\n\t"
- "adcw $0,%w0\n"
- : "=r" (b)
- : "0" (b), "r" (a));
- return b;
-}
-
-/*
- * Do a 64-bit checksum on an arbitrary memory area.
- * Returns a 32bit checksum.
- *
- * This isn't as time critical as it used to be because many NICs
- * do hardware checksumming these days.
- *
- * Things tried and found to not make it faster:
- * Manual Prefetching
- * Unrolling to an 128 bytes inner loop.
- * Using interleaving with more registers to break the carry chains.
- */
-static unsigned do_csum(const unsigned char *buff, unsigned len)
-{
- unsigned odd, count;
- unsigned long result = 0;
-
- if (unlikely(len == 0))
- return result;
- odd = 1 & (unsigned long) buff;
- if (unlikely(odd)) {
- result = *buff << 8;
- len--;
- buff++;
- }
- count = len >> 1; /* nr of 16-bit words.. */
- if (count) {
- if (2 & (unsigned long) buff) {
- result += *(unsigned short *)buff;
- count--;
- len -= 2;
- buff += 2;
- }
- count >>= 1; /* nr of 32-bit words.. */
- if (count) {
- unsigned long zero;
- unsigned count64;
- if (4 & (unsigned long) buff) {
- result += *(unsigned int *) buff;
- count--;
- len -= 4;
- buff += 4;
- }
- count >>= 1; /* nr of 64-bit words.. */
-
- /* main loop using 64byte blocks */
- zero = 0;
- count64 = count >> 3;
- while (count64) {
- asm("addq 0*8(%[src]),%[res]\n\t"
- "adcq 1*8(%[src]),%[res]\n\t"
- "adcq 2*8(%[src]),%[res]\n\t"
- "adcq 3*8(%[src]),%[res]\n\t"
- "adcq 4*8(%[src]),%[res]\n\t"
- "adcq 5*8(%[src]),%[res]\n\t"
- "adcq 6*8(%[src]),%[res]\n\t"
- "adcq 7*8(%[src]),%[res]\n\t"
- "adcq %[zero],%[res]"
- : [res] "=r" (result)
- : [src] "r" (buff), [zero] "r" (zero),
- "[res]" (result));
- buff += 64;
- count64--;
- }
-
- /* last up to 7 8byte blocks */
- count %= 8;
- while (count) {
- asm("addq %1,%0\n\t"
- "adcq %2,%0\n"
- : "=r" (result)
- : "m" (*(unsigned long *)buff),
- "r" (zero), "0" (result));
- --count;
- buff += 8;
- }
- result = add32_with_carry(result>>32,
- result&0xffffffff);
-
- if (len & 4) {
- result += *(unsigned int *) buff;
- buff += 4;
- }
- }
- if (len & 2) {
- result += *(unsigned short *) buff;
- buff += 2;
- }
- }
- if (len & 1)
- result += *buff;
- result = add32_with_carry(result>>32, result & 0xffffffff);
- if (unlikely(odd)) {
- result = from32to16(result);
- result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
- }
- return result;
-}
-
-/*
- * computes the checksum of a memory block at buff, length len,
- * and adds in "sum" (32-bit)
- *
- * returns a 32-bit number suitable for feeding into itself
- * or csum_tcpudp_magic
- *
- * this function must be called with even lengths, except
- * for the last fragment, which may be odd
- *
- * it's best to have buff aligned on a 64-bit boundary
- */
-__wsum csum_partial(const void *buff, int len, __wsum sum)
-{
- return (__force __wsum)add32_with_carry(do_csum(buff, len),
- (__force u32)sum);
-}
-
-/*
- * this routine is used for miscellaneous IP-like checksums, mainly
- * in icmp.c
- */
-__sum16 ip_compute_csum(const void *buff, int len)
-{
- return csum_fold(csum_partial(buff,len,0));
-}
-EXPORT_SYMBOL(ip_compute_csum);
-
--
2.4.6
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