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authorRobin Murphy <robin.murphy@arm.com>2020-01-15 16:42:39 +0000
committerWill Deacon <will@kernel.org>2020-01-16 15:23:29 +0000
commit5777eaed566a1d63e344d3dd8f2b5e33be20643e (patch)
tree9bf4f13c0209f26135e66073760b297ba0cac0d9 /arch/arm64/lib
parent46cf053efec6a3a5f343fead837777efe8252a46 (diff)
downloadlinux-5777eaed566a1d63e344d3dd8f2b5e33be20643e.tar.bz2
arm64: Implement optimised checksum routine
Apparently there exist certain workloads which rely heavily on software checksumming, for which the generic do_csum() implementation becomes a significant bottleneck. Therefore let's give arm64 its own optimised version - for ease of maintenance this foregoes assembly or intrisics, and is thus not actually arm64-specific, but does rely heavily on C idioms that translate well to the A64 ISA and the typical load/store capabilities of most ARMv8 CPU cores. The resulting increase in checksum throughput scales nicely with buffer size, tending towards 4x for a small in-order core (Cortex-A53), and up to 6x or more for an aggressive big core (Ampere eMAG). Reported-by: Lingyan Huang <huanglingyan2@huawei.com> Tested-by: Lingyan Huang <huanglingyan2@huawei.com> Signed-off-by: Robin Murphy <robin.murphy@arm.com> Signed-off-by: Will Deacon <will@kernel.org>
Diffstat (limited to 'arch/arm64/lib')
-rw-r--r--arch/arm64/lib/Makefile6
-rw-r--r--arch/arm64/lib/csum.c123
2 files changed, 126 insertions, 3 deletions
diff --git a/arch/arm64/lib/Makefile b/arch/arm64/lib/Makefile
index c21b936dc01d..2fc253466dbf 100644
--- a/arch/arm64/lib/Makefile
+++ b/arch/arm64/lib/Makefile
@@ -1,9 +1,9 @@
# SPDX-License-Identifier: GPL-2.0
lib-y := clear_user.o delay.o copy_from_user.o \
copy_to_user.o copy_in_user.o copy_page.o \
- clear_page.o memchr.o memcpy.o memmove.o memset.o \
- memcmp.o strcmp.o strncmp.o strlen.o strnlen.o \
- strchr.o strrchr.o tishift.o
+ clear_page.o csum.o memchr.o memcpy.o memmove.o \
+ memset.o memcmp.o strcmp.o strncmp.o strlen.o \
+ strnlen.o strchr.o strrchr.o tishift.o
ifeq ($(CONFIG_KERNEL_MODE_NEON), y)
obj-$(CONFIG_XOR_BLOCKS) += xor-neon.o
diff --git a/arch/arm64/lib/csum.c b/arch/arm64/lib/csum.c
new file mode 100644
index 000000000000..847eb725ce09
--- /dev/null
+++ b/arch/arm64/lib/csum.c
@@ -0,0 +1,123 @@
+// 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>
+
+/* Looks dumb, but generates nice-ish code */
+static u64 accumulate(u64 sum, u64 data)
+{
+ __uint128_t tmp = (__uint128_t)sum + data;
+ return tmp + (tmp >> 64);
+}
+
+unsigned int do_csum(const unsigned char *buff, int len)
+{
+ unsigned int offset, shift, sum;
+ const u64 *ptr;
+ u64 data, sum64 = 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 = READ_ONCE_NOCHECK(*ptr++);
+#ifdef __LITTLE_ENDIAN
+ data = (data >> shift) << shift;
+#else
+ data = (data << shift) >> shift;
+#endif
+
+ /*
+ * 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 = READ_ONCE_NOCHECK(*(__uint128_t *)ptr);
+ tmp2 = READ_ONCE_NOCHECK(*(__uint128_t *)(ptr + 2));
+ tmp3 = READ_ONCE_NOCHECK(*(__uint128_t *)(ptr + 4));
+ tmp4 = READ_ONCE_NOCHECK(*(__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 = READ_ONCE_NOCHECK(*(__uint128_t *)ptr);
+
+ len -= 16;
+ ptr += 2;
+
+#ifdef __LITTLE_ENDIAN
+ data = tmp >> 64;
+ sum64 = accumulate(sum64, tmp);
+#else
+ data = tmp;
+ sum64 = accumulate(sum64, tmp >> 64);
+#endif
+ }
+ if (len > 0) {
+ sum64 = accumulate(sum64, data);
+ data = READ_ONCE_NOCHECK(*ptr);
+ len -= 8;
+ }
+ /*
+ * Tail: zero any over-read bytes similarly to the head, again
+ * preserving odd/even alignment.
+ */
+ shift = len * -8;
+#ifdef __LITTLE_ENDIAN
+ data = (data << shift) >> shift;
+#else
+ data = (data >> shift) << shift;
+#endif
+ 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;
+}