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Message-Id: <20200803194022.2966806-1-nickrterrell@gmail.com>
Date: Mon, 3 Aug 2020 12:40:22 -0700
From: Nick Terrell <nickrterrell@...il.com>
To: Ingo Molnar <mingo@...nel.org>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org,
Kernel Team <Kernel-team@...com>,
Nick Terrell <nickrterrell@...il.com>,
Nick Terrell <terrelln@...com>,
Yann Collet <yann.collet.73@...il.com>,
Gao Xiang <gaoxiang25@...wei.com>,
Sven Schmidt <4sschmid@...ormatik.uni-hamburg.de>,
Andrew Morton <akpm@...ux-foundation.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH] lz4: Fix kernel decompression speed
From: Nick Terrell <terrelln@...com>
This patch replaces all memcpy() calls with LZ4_memcpy() which calls
__builtin_memcpy() so the compiler can inline it.
LZ4 relies heavily on memcpy() with a constant size being inlined. In
x86 and i386 pre-boot environments memcpy() cannot be inlined because
memcpy() doesn't get defined as __builtin_memcpy().
An equivalent patch has been applied upstream so that the next import
won't lose this change [1].
I've measured the kernel decompression speed using QEMU before and after
this patch for the x86_64 and i386 architectures. The speed-up is about
10x as shown below.
Code Arch Kernel Size Time Speed
v5.8 x86_64 11504832 B 148 ms 79 MB/s
patch x86_64 11503872 B 13 ms 885 MB/s
v5.8 i386 9621216 B 91 ms 106 MB/s
patch i386 9620224 B 10 ms 962 MB/s
I also measured the time to decompress the initramfs on x86_64, i386,
and arm. All three show the same decompression speed before and after,
as expected.
[1] https://github.com/lz4/lz4/pull/890
Signed-off-by: Nick Terrell <terrelln@...com>
Cc: Yann Collet <yann.collet.73@...il.com>
Cc: Gao Xiang <gaoxiang25@...wei.com>
Cc: Sven Schmidt <4sschmid@...ormatik.uni-hamburg.de>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
---
lib/lz4/lz4_compress.c | 4 ++--
lib/lz4/lz4_decompress.c | 18 +++++++++---------
lib/lz4/lz4defs.h | 10 ++++++++++
lib/lz4/lz4hc_compress.c | 2 +-
4 files changed, 22 insertions(+), 12 deletions(-)
diff --git a/lib/lz4/lz4_compress.c b/lib/lz4/lz4_compress.c
index cc7b6d4cc7c7..90bb67994688 100644
--- a/lib/lz4/lz4_compress.c
+++ b/lib/lz4/lz4_compress.c
@@ -446,7 +446,7 @@ static FORCE_INLINE int LZ4_compress_generic(
*op++ = (BYTE)(lastRun << ML_BITS);
}
- memcpy(op, anchor, lastRun);
+ LZ4_memcpy(op, anchor, lastRun);
op += lastRun;
}
@@ -708,7 +708,7 @@ static int LZ4_compress_destSize_generic(
} else {
*op++ = (BYTE)(lastRunSize<<ML_BITS);
}
- memcpy(op, anchor, lastRunSize);
+ LZ4_memcpy(op, anchor, lastRunSize);
op += lastRunSize;
}
diff --git a/lib/lz4/lz4_decompress.c b/lib/lz4/lz4_decompress.c
index 5371dab6b481..00cb0d0b73e1 100644
--- a/lib/lz4/lz4_decompress.c
+++ b/lib/lz4/lz4_decompress.c
@@ -153,7 +153,7 @@ static FORCE_INLINE int LZ4_decompress_generic(
&& likely((endOnInput ? ip < shortiend : 1) &
(op <= shortoend))) {
/* Copy the literals */
- memcpy(op, ip, endOnInput ? 16 : 8);
+ LZ4_memcpy(op, ip, endOnInput ? 16 : 8);
op += length; ip += length;
/*
@@ -172,9 +172,9 @@ static FORCE_INLINE int LZ4_decompress_generic(
(offset >= 8) &&
(dict == withPrefix64k || match >= lowPrefix)) {
/* Copy the match. */
- memcpy(op + 0, match + 0, 8);
- memcpy(op + 8, match + 8, 8);
- memcpy(op + 16, match + 16, 2);
+ LZ4_memcpy(op + 0, match + 0, 8);
+ LZ4_memcpy(op + 8, match + 8, 8);
+ LZ4_memcpy(op + 16, match + 16, 2);
op += length + MINMATCH;
/* Both stages worked, load the next token. */
continue;
@@ -263,7 +263,7 @@ static FORCE_INLINE int LZ4_decompress_generic(
}
}
- memcpy(op, ip, length);
+ LZ4_memcpy(op, ip, length);
ip += length;
op += length;
@@ -350,7 +350,7 @@ static FORCE_INLINE int LZ4_decompress_generic(
size_t const copySize = (size_t)(lowPrefix - match);
size_t const restSize = length - copySize;
- memcpy(op, dictEnd - copySize, copySize);
+ LZ4_memcpy(op, dictEnd - copySize, copySize);
op += copySize;
if (restSize > (size_t)(op - lowPrefix)) {
/* overlap copy */
@@ -360,7 +360,7 @@ static FORCE_INLINE int LZ4_decompress_generic(
while (op < endOfMatch)
*op++ = *copyFrom++;
} else {
- memcpy(op, lowPrefix, restSize);
+ LZ4_memcpy(op, lowPrefix, restSize);
op += restSize;
}
}
@@ -386,7 +386,7 @@ static FORCE_INLINE int LZ4_decompress_generic(
while (op < copyEnd)
*op++ = *match++;
} else {
- memcpy(op, match, mlen);
+ LZ4_memcpy(op, match, mlen);
}
op = copyEnd;
if (op == oend)
@@ -400,7 +400,7 @@ static FORCE_INLINE int LZ4_decompress_generic(
op[2] = match[2];
op[3] = match[3];
match += inc32table[offset];
- memcpy(op + 4, match, 4);
+ LZ4_memcpy(op + 4, match, 4);
match -= dec64table[offset];
} else {
LZ4_copy8(op, match);
diff --git a/lib/lz4/lz4defs.h b/lib/lz4/lz4defs.h
index 1a7fa9d9170f..c91dd96ef629 100644
--- a/lib/lz4/lz4defs.h
+++ b/lib/lz4/lz4defs.h
@@ -137,6 +137,16 @@ static FORCE_INLINE void LZ4_writeLE16(void *memPtr, U16 value)
return put_unaligned_le16(value, memPtr);
}
+/*
+ * LZ4 relies on memcpy with a constant size being inlined. In freestanding
+ * environments, the compiler can't assume the implementation of memcpy() is
+ * standard compliant, so apply its specialized memcpy() inlining logic. When
+ * possible, use __builtin_memcpy() to tell the compiler to analyze memcpy()
+ * as-if it were standard compliant, so it can inline it in freestanding
+ * environments. This is needed when decompressing the Linux Kernel, for example.
+ */
+#define LZ4_memcpy(dst, src, size) __builtin_memcpy(dst, src, size)
+
static FORCE_INLINE void LZ4_copy8(void *dst, const void *src)
{
#if LZ4_ARCH64
diff --git a/lib/lz4/lz4hc_compress.c b/lib/lz4/lz4hc_compress.c
index 1b61d874e337..e7ac8694b797 100644
--- a/lib/lz4/lz4hc_compress.c
+++ b/lib/lz4/lz4hc_compress.c
@@ -570,7 +570,7 @@ static int LZ4HC_compress_generic(
*op++ = (BYTE) lastRun;
} else
*op++ = (BYTE)(lastRun<<ML_BITS);
- memcpy(op, anchor, iend - anchor);
+ LZ4_memcpy(op, anchor, iend - anchor);
op += iend - anchor;
}
--
2.28.0
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