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lz4: fix kernel decompression speed

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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@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Yann Collet <yann.collet.73@gmail.com>
Cc: Gao Xiang <gaoxiang25@huawei.com>
Cc: Sven Schmidt <4sschmid@informatik.uni-hamburg.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Arvind Sankar <nivedita@alum.mit.edu>
Link: http://lkml.kernel.org/r/20200803194022.2966806-1-nickrterrell@gmail.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Nick Terrell 2020-08-14 17:30:10 -07:00 committed by Linus Torvalds
parent a8a4b7aeaf
commit b1a3e75e46
4 changed files with 22 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
lib/lz4/lz4_compress.c
View File

@ -446,7 +446,7 @@ _last_literals:
*op++ = (BYTE)(lastRun << ML_BITS);
}
memcpy(op, anchor, lastRun);
LZ4_memcpy(op, anchor, lastRun);
op += lastRun;
}
@ -708,7 +708,7 @@ _last_literals:
} else {
*op++ = (BYTE)(lastRunSize<<ML_BITS);
}
memcpy(op, anchor, lastRunSize);
LZ4_memcpy(op, anchor, lastRunSize);
op += lastRunSize;
}

18
lib/lz4/lz4_decompress.c
View File

@ -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 @@ _copy_match:
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 @@ _copy_match:
while (op < endOfMatch)
*op++ = *copyFrom++;
} else {
memcpy(op, lowPrefix, restSize);
LZ4_memcpy(op, lowPrefix, restSize);
op += restSize;
}
}
@ -386,7 +386,7 @@ _copy_match:
while (op < copyEnd)
*op++ = *match++;
} else {
memcpy(op, match, mlen);
LZ4_memcpy(op, match, mlen);
}
op = copyEnd;
if (op == oend)
@ -400,7 +400,7 @@ _copy_match:
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);

10
lib/lz4/lz4defs.h
View File

@ -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

2
lib/lz4/lz4hc_compress.c
View File

@ -570,7 +570,7 @@ _Search3:
*op++ = (BYTE) lastRun;
} else
*op++ = (BYTE)(lastRun<<ML_BITS);
memcpy(op, anchor, iend - anchor);
LZ4_memcpy(op, anchor, iend - anchor);
op += iend - anchor;
}