[PATCH v3] LoongArch: add checksum optimization for 64-bit system

From: Bibo Mao
Date: Thu Feb 16 2023 - 08:09:24 EST


loongArch platform is 64-bit system, which supports 8 bytes memory
accessing, generic checksum function uses 4 byte memory access.
This patch adds 8-bytes memory access optimization for checksum
function on loongArch. And the code comes from arm64 system.

When network hw checksum is disabled, iperf performance improves
about 10% with this patch.

Signed-off-by: Bibo Mao <maobibo@xxxxxxxxxxx>
---
Changelog:
v3: modify function accumulate() to handle better on loongarch platform,
maybe it's compiler optimization issue.
v2: use rotation API in function csum_fold to reduce one instruction.
---
arch/loongarch/include/asm/checksum.h | 65 ++++++++++++
arch/loongarch/lib/Makefile | 2 +-
arch/loongarch/lib/csum.c | 141 ++++++++++++++++++++++++++
3 files changed, 207 insertions(+), 1 deletion(-)
create mode 100644 arch/loongarch/include/asm/checksum.h
create mode 100644 arch/loongarch/lib/csum.c

diff --git a/arch/loongarch/include/asm/checksum.h b/arch/loongarch/include/asm/checksum.h
new file mode 100644
index 000000000000..8a7d368d801d
--- /dev/null
+++ b/arch/loongarch/include/asm/checksum.h
@@ -0,0 +1,65 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2016 ARM Ltd.
+ * Copyright (C) 2023 Loongson Technology Corporation Limited
+ */
+#ifndef __ASM_CHECKSUM_H
+#define __ASM_CHECKSUM_H
+
+#include <linux/in6.h>
+
+#define _HAVE_ARCH_IPV6_CSUM
+__sum16 csum_ipv6_magic(const struct in6_addr *saddr,
+ const struct in6_addr *daddr,
+ __u32 len, __u8 proto, __wsum sum);
+
+/*
+ * turns a 32-bit partial checksum (e.g. from csum_partial) into a
+ * 1's complement 16-bit checksum.
+ */
+static inline __sum16 csum_fold(__wsum sum)
+{
+ u32 tmp = (__force u32)sum;
+
+ /*
+ * swap the two 16-bit halves of sum
+ * if there is a carry from adding the two 16-bit halves,
+ * it will carry from the lower half into the upper half,
+ * giving us the correct sum in the upper half.
+ */
+ return (__force __sum16)(~(tmp + rol32(tmp, 16)) >> 16);
+}
+#define csum_fold csum_fold
+
+/*
+ * This is a version of ip_compute_csum() optimized for IP headers,
+ * which always checksum on 4 octet boundaries. ihl is the number
+ * of 32-bit words and is always >= 5.
+ */
+static inline __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
+{
+ __uint128_t tmp;
+ u64 sum;
+ int n = ihl; /* we want it signed */
+
+ tmp = *(const __uint128_t *)iph;
+ iph += 16;
+ n -= 4;
+ tmp += ((tmp >> 64) | (tmp << 64));
+ sum = tmp >> 64;
+ do {
+ sum += *(const u32 *)iph;
+ iph += 4;
+ } while (--n > 0);
+
+ sum += ror64(sum, 32);
+ return csum_fold((__force __wsum)(sum >> 32));
+}
+#define ip_fast_csum ip_fast_csum
+
+extern unsigned int do_csum(const unsigned char *buff, int len);
+#define do_csum do_csum
+
+#include <asm-generic/checksum.h>
+
+#endif /* __ASM_CHECKSUM_H */
diff --git a/arch/loongarch/lib/Makefile b/arch/loongarch/lib/Makefile
index 40bde632900f..6ba6df411f90 100644
--- a/arch/loongarch/lib/Makefile
+++ b/arch/loongarch/lib/Makefile
@@ -4,4 +4,4 @@
#

lib-y += delay.o memset.o memcpy.o memmove.o \
- clear_user.o copy_user.o dump_tlb.o unaligned.o
+ clear_user.o copy_user.o dump_tlb.o unaligned.o csum.o
diff --git a/arch/loongarch/lib/csum.c b/arch/loongarch/lib/csum.c
new file mode 100644
index 000000000000..a5e84b403c3b
--- /dev/null
+++ b/arch/loongarch/lib/csum.c
@@ -0,0 +1,141 @@
+// SPDX-License-Identifier: GPL-2.0-only
+// Copyright (C) 2019-2020 Arm Ltd.
+
+#include <linux/compiler.h>
+#include <linux/kasan-checks.h>
+#include <linux/kernel.h>
+
+#include <net/checksum.h>
+
+static u64 accumulate(u64 sum, u64 data)
+{
+ sum += data;
+ if (sum < data)
+ sum += 1;
+ return sum;
+}
+
+/*
+ * We over-read the buffer and this makes KASAN unhappy. Instead, disable
+ * instrumentation and call kasan explicitly.
+ */
+unsigned int __no_sanitize_address do_csum(const unsigned char *buff, int len)
+{
+ unsigned int offset, shift, sum;
+ const u64 *ptr;
+ u64 data, sum64 = 0;
+
+ if (unlikely(len == 0))
+ return 0;
+
+ offset = (unsigned long)buff & 7;
+ /*
+ * This is to all intents and purposes safe, since rounding down cannot
+ * result in a different page or cache line being accessed, and @buff
+ * should absolutely not be pointing to anything read-sensitive. We do,
+ * however, have to be careful not to piss off KASAN, which means using
+ * unchecked reads to accommodate the head and tail, for which we'll
+ * compensate with an explicit check up-front.
+ */
+ kasan_check_read(buff, len);
+ ptr = (u64 *)(buff - offset);
+ len = len + offset - 8;
+
+ /*
+ * Head: zero out any excess leading bytes. Shifting back by the same
+ * amount should be at least as fast as any other way of handling the
+ * odd/even alignment, and means we can ignore it until the very end.
+ */
+ shift = offset * 8;
+ data = *ptr++;
+ data = (data >> shift) << shift;
+
+ /*
+ * Body: straightforward aligned loads from here on (the paired loads
+ * underlying the quadword type still only need dword alignment). The
+ * main loop strictly excludes the tail, so the second loop will always
+ * run at least once.
+ */
+ while (unlikely(len > 64)) {
+ __uint128_t tmp1, tmp2, tmp3, tmp4;
+
+ tmp1 = *(__uint128_t *)ptr;
+ tmp2 = *(__uint128_t *)(ptr + 2);
+ tmp3 = *(__uint128_t *)(ptr + 4);
+ tmp4 = *(__uint128_t *)(ptr + 6);
+
+ len -= 64;
+ ptr += 8;
+
+ /* This is the "don't dump the carry flag into a GPR" idiom */
+ tmp1 += (tmp1 >> 64) | (tmp1 << 64);
+ tmp2 += (tmp2 >> 64) | (tmp2 << 64);
+ tmp3 += (tmp3 >> 64) | (tmp3 << 64);
+ tmp4 += (tmp4 >> 64) | (tmp4 << 64);
+ tmp1 = ((tmp1 >> 64) << 64) | (tmp2 >> 64);
+ tmp1 += (tmp1 >> 64) | (tmp1 << 64);
+ tmp3 = ((tmp3 >> 64) << 64) | (tmp4 >> 64);
+ tmp3 += (tmp3 >> 64) | (tmp3 << 64);
+ tmp1 = ((tmp1 >> 64) << 64) | (tmp3 >> 64);
+ tmp1 += (tmp1 >> 64) | (tmp1 << 64);
+ tmp1 = ((tmp1 >> 64) << 64) | sum64;
+ tmp1 += (tmp1 >> 64) | (tmp1 << 64);
+ sum64 = tmp1 >> 64;
+ }
+ while (len > 8) {
+ __uint128_t tmp;
+
+ sum64 = accumulate(sum64, data);
+ tmp = *(__uint128_t *)ptr;
+
+ len -= 16;
+ ptr += 2;
+
+ data = tmp >> 64;
+ sum64 = accumulate(sum64, tmp);
+ }
+ if (len > 0) {
+ sum64 = accumulate(sum64, data);
+ data = *ptr;
+ len -= 8;
+ }
+ /*
+ * Tail: zero any over-read bytes similarly to the head, again
+ * preserving odd/even alignment.
+ */
+ shift = len * -8;
+ data = (data << shift) >> shift;
+ sum64 = accumulate(sum64, data);
+
+ /* Finally, folding */
+ sum64 += (sum64 >> 32) | (sum64 << 32);
+ sum = sum64 >> 32;
+ sum += (sum >> 16) | (sum << 16);
+ if (offset & 1)
+ return (u16)swab32(sum);
+
+ return sum >> 16;
+}
+
+__sum16 csum_ipv6_magic(const struct in6_addr *saddr,
+ const struct in6_addr *daddr,
+ __u32 len, __u8 proto, __wsum csum)
+{
+ __uint128_t src, dst;
+ u64 sum = (__force u64)csum;
+
+ src = *(const __uint128_t *)saddr->s6_addr;
+ dst = *(const __uint128_t *)daddr->s6_addr;
+
+ sum += (__force u32)htonl(len);
+ sum += (u32)proto << 24;
+ src += (src >> 64) | (src << 64);
+ dst += (dst >> 64) | (dst << 64);
+
+ sum = accumulate(sum, src >> 64);
+ sum = accumulate(sum, dst >> 64);
+
+ sum += ((sum >> 32) | (sum << 32));
+ return csum_fold((__force __wsum)(sum >> 32));
+}
+EXPORT_SYMBOL(csum_ipv6_magic);
--
2.27.0