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Message-ID: <688724e9-d505-38c6-b30a-74e49dc8d353@163.com>
Date: Wed, 18 Nov 2020 23:10:27 +0800
From: Zhaoxiu Zeng <zengzhaoxiu@....com>
To: Christoph Hellwig <hch@...radead.org>
Cc: Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
linux-arch@...r.kernel.org, Zhaoxiu Zeng <zhaoxiu.zeng@...il.com>
Subject: Re: [PATCH 1/3] lib: Introduce copy_from_back()
在 2020/11/17 1:24, Christoph Hellwig 写道:
>> +#define FAST_COPY_SAFEGUARD_SIZE (sizeof(long) * 2 - 1)
>> +
>> +#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
>> +
>> +/*
>> + * The caller must ensure that the output buffer has enough space (len + FAST_COPY_SAFEGUARD_SIZE),
>> + * so we can write 2 words per loop without overflowing the output buffer
>> + */
>> +static __always_inline u8 *copy_from_back_fast(u8 *out, size_t dist, size_t len)
>
> The code is pretty unreadable with these longs lines. Please stick to
> the normal 80 char limit.
>
I cleaned up the code.
---
include/asm-generic/Kbuild | 1 +
include/asm-generic/copy_from_back.h | 422 +++++++++++++++++++++++++++
2 files changed, 423 insertions(+)
create mode 100644 include/asm-generic/copy_from_back.h
diff --git a/include/asm-generic/Kbuild b/include/asm-generic/Kbuild
index e78bbb9a07e9..84964a32572c 100644
--- a/include/asm-generic/Kbuild
+++ b/include/asm-generic/Kbuild
@@ -12,6 +12,7 @@ mandatory-y += bugs.h
mandatory-y += cacheflush.h
mandatory-y += checksum.h
mandatory-y += compat.h
+mandatory-y += copy_from_back.h
mandatory-y += current.h
mandatory-y += delay.h
mandatory-y += device.h
diff --git a/include/asm-generic/copy_from_back.h b/include/asm-generic/copy_from_back.h
new file mode 100644
index 000000000000..5628290f0286
--- /dev/null
+++ b/include/asm-generic/copy_from_back.h
@@ -0,0 +1,423 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __COPY_FROM_BACK_H
+#define __COPY_FROM_BACK_H
+
+#include <linux/types.h>
+
+#define FAST_COPY_SAFEGUARD_SIZE (sizeof(long) * 2 - 1)
+
+#define COPY_WORD(ptr) \
+ *(unsigned long *)(ptr) = *(unsigned long *)((ptr) - dist)
+
+#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
+
+/*
+ * The caller must ensure that the output buffer has enough space
+ * (len + FAST_COPY_SAFEGUARD_SIZE), so we can write 2 words per
+ * loop without overflowing the output buffer
+ */
+static __always_inline u8 *copy_from_back_fast(u8 *out, size_t dist, size_t len)
+{
+ u8 *end = out + len;
+
+ /*
+ * ensure the distance is larger than sizeof(long),
+ * so we can copy one word per step
+ */
+ if (unlikely(dist < sizeof(long))) {
+#if BITS_PER_LONG == 32
+ /* extend the distance '1,2,3' to '4,4,6' */
+ out[0] = out[0 - dist];
+ out[1] = out[1 - dist];
+ out[2] = out[2 - dist];
+ out += sizeof(long) - 1;
+ if (out >= end)
+ return end;
+ dist = dist == 3 ? 6 : 4;
+#elif BITS_PER_LONG == 64
+ /* extend the distance '1,2,3,4,5,6,7' to '8,8,9,8,A,C,E' */
+ out[0] = out[0 - dist];
+ out[1] = out[1 - dist];
+ out[2] = out[2 - dist];
+ *(u32 *)(out + 3) = *(u32 *)(out -
+ ((0x43213110 >> (dist * 4)) & 0xF));
+ out += sizeof(long) - 1;
+ if (out >= end)
+ return end;
+ dist = (0xECA89880 >> (dist * 4)) & 0xF;
+#else
+#error "Unknown BITS_PER_LONG"
+#endif
+ }
+
+ do {
+ COPY_WORD(out);
+ out += sizeof(long);
+ COPY_WORD(out);
+ out += sizeof(long);
+ } while (out < end);
+
+ return end;
+}
+
+static __always_inline u8 *copy_from_back(u8 *out, size_t dist, size_t len)
+{
+ if (len >= sizeof(long)) {
+ /* extend the distance if nedded */
+ if (unlikely(dist < sizeof(long))) {
+#if BITS_PER_LONG == 32
+ out[0] = out[0 - dist];
+ out[1] = out[1 - dist];
+ out[2] = out[2 - dist];
+ out += sizeof(long) - 1;
+ len -= sizeof(long) - 1;
+ if (len < sizeof(long))
+ goto _last;
+ dist = dist == 3 ? 6 : 4;
+#elif BITS_PER_LONG == 64
+ out[0] = out[0 - dist];
+ out[1] = out[1 - dist];
+ out[2] = out[2 - dist];
+ *(u32 *)(out + 3) = *(u32 *)(out -
+ ((0x43213110 >> (dist * 4)) & 0xF));
+ out += sizeof(long) - 1;
+ len -= sizeof(long) - 1;
+ if (len < sizeof(long))
+ goto _last;
+ dist = (0xECA89880 >> (dist * 4)) & 0xF;
+#else
+#error "Unknown BITS_PER_LONG"
+#endif
+ }
+
+ while (len >= sizeof(long) * 2) {
+ len -= sizeof(long) * 2;
+ COPY_WORD(out);
+ out += sizeof(long);
+ COPY_WORD(out);
+ out += sizeof(long);
+ }
+ if (len >= sizeof(long)) {
+ len -= sizeof(long);
+ COPY_WORD(out);
+ out += sizeof(long);
+ }
+ if (len) {
+ out += len;
+ COPY_WORD(out - sizeof(long));
+ }
+ } else {
+ *out = *(out - dist);
+ out++;
+ len--;
+_last:
+ if (len >= 2) {
+ if (dist == 1)
+ dist = 2;
+#if BITS_PER_LONG == 32
+ *(u16 *)out = *(u16 *)(out - dist);
+ out += 2;
+ len -= 2;
+#else
+ do {
+ *(u16 *)out = *(u16 *)(out - dist);
+ out += 2;
+ len -= 2;
+ } while (len >= 2);
+#endif
+ }
+ if (len) {
+ *out = *(out - dist);
+ out++;
+ }
+ }
+
+ return out;
+}
+
+#else /* CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS */
+
+#include <asm/unaligned.h>
+
+/*
+ * Endian independent macros for shifting bits
+ */
+#ifdef __BIG_ENDIAN
+# define LSPULL(x, n) ((x) << (n))
+# define LSPUSH(x, n) ((x) >> (n))
+# define LSMASK(n) (~(~0UL >> (n)))
+# define LSFETCH(x, n) ((x) >> (BITS_PER_LONG - (n)))
+#else
+# define LSPULL(x, n) ((x) >> (n))
+# define LSPUSH(x, n) ((x) << (n))
+# define LSMASK(n) ((1UL << (n)) - 1)
+# define LSFETCH(x, n) ((x) & LSMASK(n))
+#endif
+
+#define COPY_WORD_SHIFT(ptr, l, h) \
+ *(unsigned long *)(ptr) = LSPULL((l), shift_l) | LSPUSH((h), shift_h)
+
+static __always_inline u8 *copy_from_back_fast(u8 *out, size_t dist, size_t len)
+{
+ u8 *end = out + len;
+ unsigned long val;
+ unsigned int n;
+
+ /* extend the distance if nedded */
+ if (unlikely(dist < sizeof(long))) {
+#if BITS_PER_LONG == 32
+ out[0] = out[0 - dist];
+ out[1] = out[1 - dist];
+ out[2] = out[2 - dist];
+ out += sizeof(long) - 1;
+ if (out >= end)
+ return end;
+ dist = dist == 3 ? 6 : 4;
+#elif BITS_PER_LONG == 64
+ out[0] = out[0 - dist];
+ out[1] = out[1 - dist];
+ out[2] = out[2 - dist];
+ out[3] = out[3 - dist];
+ out[4] = out[4 - dist];
+ out[5] = out[5 - dist];
+ out[6] = out[6 - dist];
+ out += sizeof(long) - 1;
+ if (out >= end)
+ return end;
+ dist = (0xECA89880 >> (dist * 4)) & 0xF;
+#else
+#error "Unknown BITS_PER_LONG"
+#endif
+ }
+
+ /* align out addr */
+ n = (uintptr_t)out & (sizeof(long) - 1);
+ if (n) {
+ val = get_unaligned((unsigned long *)(out - dist));
+ put_unaligned(val, (unsigned long *)out);
+ out += sizeof(long);
+ if (out >= end)
+ return end;
+ out -= n;
+ }
+
+ n = dist & (sizeof(long) - 1);
+ if (n) {
+ const unsigned int shift_h = n * 8;
+ const unsigned int shift_l = BITS_PER_LONG - shift_h;
+ unsigned long prev;
+
+ dist -= n;
+ prev = *(unsigned long *)(out - dist - sizeof(long));
+
+ do {
+ val = *(unsigned long *)(out - dist);
+ COPY_WORD_SHIFT(out, prev, val);
+ out += sizeof(long);
+ prev = *(unsigned long *)(out - dist);
+ COPY_WORD_SHIFT(out, val, prev);
+ out += sizeof(long);
+ } while (out < end);
+ } else {
+ do {
+ COPY_WORD(out);
+ out += sizeof(long);
+ COPY_WORD(out);
+ out += sizeof(long);
+ } while (out < end);
+ }
+
+ return end;
+}
+
+static __always_inline u8 *copy_from_back(u8 *out, size_t dist, size_t len)
+{
+ if (len >= sizeof(long)) {
+ unsigned long val;
+ unsigned int n;
+
+ /* extend the distance if nedded */
+ if (unlikely(dist < sizeof(long))) {
+#if BITS_PER_LONG == 32
+ out[0] = out[0 - dist];
+ out[1] = out[1 - dist];
+ out[2] = out[2 - dist];
+ out += sizeof(long) - 1;
+ len -= sizeof(long) - 1;
+ if (len < sizeof(long))
+ goto _last;
+ dist = dist == 3 ? 6 : 4;
+#elif BITS_PER_LONG == 64
+ out[0] = out[0 - dist];
+ out[1] = out[1 - dist];
+ out[2] = out[2 - dist];
+ out[3] = out[3 - dist];
+ out[4] = out[4 - dist];
+ out[5] = out[5 - dist];
+ out[6] = out[6 - dist];
+ out += sizeof(long) - 1;
+ len -= sizeof(long) - 1;
+ if (len < sizeof(long))
+ goto _last;
+ dist = (0xECA89880 >> (dist * 4)) & 0xF;
+#else
+#error "Unknown BITS_PER_LONG"
+#endif
+ }
+
+ /* align out addr */
+ n = (uintptr_t)out & (sizeof(long) - 1);
+ if (n) {
+ val = get_unaligned((unsigned long *)(out - dist));
+ put_unaligned(val, (unsigned long *)out);
+ out += sizeof(long);
+ len -= sizeof(long);
+ if (len < sizeof(long)) {
+ if (len)
+ goto _last;
+ return out;
+ }
+ out -= n;
+ len += n;
+ }
+
+ n = dist & (sizeof(long) - 1);
+ if (n) {
+ const unsigned int shift_h = n * 8;
+ const unsigned int shift_l = BITS_PER_LONG - shift_h;
+ unsigned long prev;
+
+ dist -= n;
+ prev = *(unsigned long *)(out - dist - sizeof(long));
+
+ while (len >= sizeof(long) * 2) {
+ len -= sizeof(long) * 2;
+ val = *(unsigned long *)(out - dist);
+ COPY_WORD_SHIFT(out, prev, val);
+ out += sizeof(long);
+ prev = *(unsigned long *)(out - dist);
+ COPY_WORD_SHIFT(out, val, prev);
+ out += sizeof(long);
+ }
+ if (len >= sizeof(long)) {
+ len -= sizeof(long);
+ val = *(unsigned long *)(out - dist);
+ COPY_WORD_SHIFT(out, prev, val);
+ out += sizeof(long);
+ prev = val;
+ }
+ if (len) {
+ val = LSPULL(prev, shift_l);
+ if (len * 8 > shift_h) {
+ prev = *(unsigned long *)(out - dist);
+ val |= LSPUSH(prev, shift_h);
+ }
+ goto _part;
+ }
+ } else if (dist != sizeof(long)) {
+ while (len >= sizeof(long) * 2) {
+ len -= sizeof(long) * 2;
+ COPY_WORD(out);
+ out += sizeof(long);
+ COPY_WORD(out);
+ out += sizeof(long);
+ }
+ if (len >= sizeof(long)) {
+ len -= sizeof(long);
+ COPY_WORD(out);
+ out += sizeof(long);
+ }
+ if (len) {
+ val = *(unsigned long *)(out - dist);
+ goto _part;
+ }
+ } else {
+ val = *(unsigned long *)(out - sizeof(long));
+ while (len >= sizeof(long) * 2) {
+ len -= sizeof(long) * 2;
+ *(unsigned long *)out = val;
+ out += sizeof(long);
+ *(unsigned long *)out = val;
+ out += sizeof(long);
+ }
+ if (len >= sizeof(long)) {
+ len -= sizeof(long);
+ *(unsigned long *)out = val;
+ out += sizeof(long);
+ }
+ if (len) {
+_part:
+#if BITS_PER_LONG == 64
+ if (len & 4) {
+ *(u32 *)out = LSFETCH(val, 32);
+ out += 4;
+ val = LSPULL(val, 32);
+ }
+#endif
+ if (len & 2) {
+ *(u16 *)out = LSFETCH(val, 16);
+ out += 2;
+ val = LSPULL(val, 16);
+ }
+ if (len & 1)
+ *out++ = LSFETCH(val, 8);
+ }
+ }
+ } else {
+_last:
+ /* align out addr */
+ if ((uintptr_t)out & 1) {
+ *out = *(out - dist);
+ out++;
+ len--;
+ }
+ if (len >= 2) {
+#if BITS_PER_LONG == 32
+ if (dist > 1)
+ *(u16 *)out = get_unaligned((u16 *)(out - dist));
+ else
+ *(u16 *)out = out[-1] | out[-1] << 8;
+ out += 2;
+ len -= 2;
+#else
+ u16 val;
+
+ if (dist > 2) {
+ do {
+ val = get_unaligned((u16 *)(out - dist));
+ *(u16 *)out = val;
+ out += 2;
+ len -= 2;
+ } while (len >= 2);
+ } else {
+ val = dist == 2 ? *(u16 *)(out - 2)
+ : (out[-1] | out[-1] << 8);
+ do {
+ *(u16 *)out = val;
+ out += 2;
+ len -= 2;
+ } while (len >= 2);
+ }
+#endif
+ }
+ if (len) {
+ *out = *(out - dist);
+ out++;
+ }
+ }
+
+ return out;
+}
+
+#undef COPY_WORD_SHIFT
+
+#undef LSPULL
+#undef LSPUSH
+#undef LSMASK
+#undef LSFETCH
+
+#endif /* CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS */
+
+#undef COPY_WORD
+
+#endif /* __COPY_FROM_BACK_H */
--
2.28.0
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