Re: [PATCH v4 2/5] lib/lz4: update LZ4 decompressor module

Gao Xiang
2024-05-28T14:03:48Z

On 2024/5/28 21:28, Jonathan Liu wrote:
> Hi Jianan,
>
> Here are the LZ4 decompression times I got running "time unlz4 ..." on
> Rock 4 SE with RK3399 CPU.
>
> v2024.04: 1.329 seconds
> v2024.04 with 26c7fdadcb7 ("lib/lz4: update LZ4 decompressor module")
> reverted: 0.665 seconds
> v2024.04 with your patch: 1.216 seconds
>
> I managed to get better performance by optimizing it myself.
> v2024.04 with my patch: 0.785 seconds
>
> With my patch, it makes no difference if I use __builtin_memcpy or
> memcpy in lz4.c and lz4_wrapper.c so I just left it using memcpy.
> It is still slower than reverting the LZ4 update though.

I'm not sure what's the old version come from, but from the copyright
itself it seems some earlier 2015 version. Note that there is no
absolute outperform between old version and new version, old version
may be lack of some necessary boundary check or lead to some msan
warning or something, like a new commit of year 2016:
https://github.com/lz4/lz4/commit/f094f531441140f10fd461ba769f49d10f5cd581

/* costs ~1%; silence an msan warning when offset == 0 */
/*
* note : when partialDecoding, there is no guarantee that
* at least 4 bytes remain available in output buffer
*/
if (!partialDecoding) {
assert(oend > op);
assert(oend - op >= 4);

LZ4_write32(op, (U32)offset);
}
For the example above, you could completely remove the line above if
you don't care about such warning, as it claims ~1% performance loss.

Also since no u-boot user uses in-place decompression and if
you memmove() doesn't behave well, you could update the
following line
/*
* supports overlapping memory regions; only matters
* for in-place decompression scenarios
*/
memmove(op, ip, length);
into memcpy() instead.

The new lz4 codebase relies on memcpy() / memmove() code optimization
more than old version, if memcpy() assembly doesn't generate well on
your platform, it might have some issue.

Thanks,
Gao Xiang

>
> My patch:
> --- a/lib/lz4.c
> +++ b/lib/lz4.c
> @@ -41,6 +41,16 @@ static FORCE_INLINE u16 LZ4_readLE16(const void *src)
> return get_unaligned_le16(src);
> }
>
> +static FORCE_INLINE void LZ4_copy2(void *dst, const void *src)
> +{
> + put_unaligned(get_unaligned((const u16 *)src), (u16 *)dst);
> +}
> +
> +static FORCE_INLINE void LZ4_copy4(void *dst, const void *src)
> +{
> + put_unaligned(get_unaligned((const u32 *)src), (u32 *)dst);
> +}
> +
> static FORCE_INLINE void LZ4_copy8(void *dst, const void *src)
> {
> put_unaligned(get_unaligned((const u64 *)src), (u64 *)dst);
> @@ -215,7 +225,10 @@ static FORCE_INLINE int LZ4_decompress_generic(
> && likely((endOnInput ? ip < shortiend : 1) &
> (op <= shortoend))) {
> /* Copy the literals */
> - memcpy(op, ip, endOnInput ? 16 : 8);
> + LZ4_copy8(op, ip);
> + if (endOnInput)
> + LZ4_copy8(op + 8, ip + 8);
> +
> op += length; ip += length;
>
> /*
> @@ -234,9 +247,9 @@ 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_copy8(op, match);
> + LZ4_copy8(op + 8, match + 8);
> + LZ4_copy2(op + 16, match + 16);
> op += length + MINMATCH;
> /* Both stages worked, load the next token. */
> continue;
> @@ -466,7 +479,7 @@ _copy_match:
> op[2] = match[2];
> op[3] = match[3];
> match += inc32table[offset];
> - memcpy(op + 4, match, 4);
> + LZ4_copy4(op + 4, match);
> match -= dec64table[offset];
> } else {
> LZ4_copy8(op, match);
>
> Let me know if you have any further suggestions.
>
> Thanks.
>
> Regards,
> Jonathan
>
> On Sun, 26 May 2024 at 22:18, Jianan Huang <jnhuang95@gmail.com> wrote:
>>
>> Hi Jonathan,
>>
>> Could you please try the following patch ? It replaces all memcpy() calls in lz4 with __builtin_memcpy().
>>
>> diff --git a/lib/lz4.c b/lib/lz4.c
>> index d365dc727c..2afe31c1c3 100644
>> --- a/lib/lz4.c
>> +++ b/lib/lz4.c
>> @@ -34,6 +34,8 @@
>> #include <asm/unaligned.h>
>> #include <u-boot/lz4.h>
>>
>> +#define LZ4_memcpy(dst, src, size) __builtin_memcpy(dst, src, size)
>> +
>> #define FORCE_INLINE inline __attribute__((always_inline))
>>
>> static FORCE_INLINE u16 LZ4_readLE16(const void *src)
>> @@ -215,7 +217,7 @@ 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;
>>
>> /*
>> @@ -234,9 +236,9 @@ 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;
>> @@ -416,7 +418,7 @@ _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 */
>> @@ -426,7 +428,7 @@ _copy_match:
>> while (op < endOfMatch)
>> *op++ = *copyFrom++;
>> } else {
>> - memcpy(op, lowPrefix, restSize);
>> + LZ4_memcpy(op, lowPrefix, restSize);
>> op += restSize;
>> }
>> }
>> @@ -452,7 +454,7 @@ _copy_match:
>> while (op < copyEnd)
>> *op++ = *match++;
>> } else {
>> - memcpy(op, match, mlen);
>> + LZ4_memcpy(op, match, mlen);
>> }
>> op = copyEnd;
>> if (op == oend)
>> @@ -466,7 +468,7 @@ _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);
>> diff --git a/lib/lz4_wrapper.c b/lib/lz4_wrapper.c
>> index 4d48e7b0e8..e09c8d7057 100644
>> --- a/lib/lz4_wrapper.c
>> +++ b/lib/lz4_wrapper.c
>> @@ -80,7 +80,7 @@ int ulz4fn(const void *src, size_t srcn, void *dst, size_t *dstn)
>>
>> if (block_header & LZ4F_BLOCKUNCOMPRESSED_FLAG) {
>> size_t size = min((ptrdiff_t)block_size, (ptrdiff_t)(end - out));
>> - memcpy(out, in, size);
>> + LZ4_memcpy(out, in, size);
>> out += size;
>> if (size < block_size) {
>> ret = -ENOBUFS; /* output overrun */
>>
>>
>> Thanks,
>>
>> Jianan
>>
>> On 2024/5/26 16:06, Jonathan Liu wrote:
>>
>> Hi Gao,
>>
>> On Sat, 25 May 2024 at 02:52, Gao Xiang <hsiangkao@linux.alibaba.com> wrote:
>>
>> Hi,
>>
>> On 2024/5/24 22:26, Jonathan Liu wrote:
>>
>> Hi Jianan,
>>
>> On Sat, 26 Feb 2022 at 18:05, Huang Jianan <jnhuang95@gmail.com> wrote:
>>
>> Update the LZ4 compression module based on LZ4 v1.8.3 in order to
>> use the newest LZ4_decompress_safe_partial() which can now decode
>> exactly the nb of bytes requested.
>>
>> Signed-off-by: Huang Jianan <jnhuang95@gmail.com>
>>
>> I noticed after this commit LZ4 decompression is slower.
>> ulz4fn function call takes 1.209670 seconds with this commit.
>> After reverting this commit, the ulz4fn function call takes 0.587032 seconds.
>>
>> I am decompressing a LZ4 compressed kernel (compressed with lz4 v1.9.4
>> using -9 option for maximum compression) on RK3399.
>>
>> Any ideas why it is slower with this commit and how the performance
>> regression can be fixed?
>>
>> Just the quick glance, I think the issue may be due to memcpy/memmove
>> since it seems the main difference between these two codebases
>> (I'm not sure which LZ4 version the old codebase was based on) and
>> the new version mainly relies on memcpy/memmove instead of its own
>> versions.
>>
>> Would you mind to check the assembly how memcpy/memset is generated
>> on your platform?
>>
>> Here is the assembly (-mcpu=cortex-a72.cortex-a53 -march=armv8-a+crc+crypto):
>> 000000000028220c <memset>:
>> #if !CONFIG_IS_ENABLED(TINY_MEMSET)
>> unsigned long cl = 0;
>> int i;
>>
>> /* do it one word at a time (32 bits or 64 bits) while possible */
>> if ( ((ulong)s & (sizeof(*sl) - 1)) == 0) {
>> 28220c: f2400803 ands x3, x0, #0x7
>> 282210: 540002c1 b.ne 282268 <memset+0x5c> // b.any
>> for (i = 0; i < sizeof(*sl); i++) {
>> cl <<= 8;
>> cl |= c & 0xff;
>> 282214: 92401c26 and x6, x1, #0xff
>> unsigned long cl = 0;
>> 282218: d2800004 mov x4, #0x0 // #0
>> 28221c: 52800105 mov w5, #0x8 // #8
>> cl |= c & 0xff;
>> 282220: aa0420c4 orr x4, x6, x4, lsl #8
>> for (i = 0; i < sizeof(*sl); i++) {
>> 282224: 710004a5 subs w5, w5, #0x1
>> 282228: 54ffffc1 b.ne 282220 <memset+0x14> // b.any
>> }
>> while (count >= sizeof(*sl)) {
>> 28222c: cb030045 sub x5, x2, x3
>> 282230: f1001cbf cmp x5, #0x7
>> 282234: 54000148 b.hi 28225c <memset+0x50> // b.pmore
>> 282238: d343fc43 lsr x3, x2, #3
>> 28223c: 928000e4 mov x4, #0xfffffffffffffff8 // #-8
>> 282240: 9b047c63 mul x3, x3, x4
>> 282244: 8b030042 add x2, x2, x3
>> 282248: cb030003 sub x3, x0, x3
>> unsigned long *sl = (unsigned long *) s;
>> 28224c: d2800004 mov x4, #0x0 // #0
>> count -= sizeof(*sl);
>> }
>> }
>> #endif /* fill 8 bits at a time */
>> s8 = (char *)sl;
>> while (count--)
>> 282250: eb04005f cmp x2, x4
>> 282254: 540000e1 b.ne 282270 <memset+0x64> // b.any
>> *s8++ = c;
>>
>> return s;
>> }
>> 282258: d65f03c0 ret
>> *sl++ = cl;
>> 28225c: f8236804 str x4, [x0, x3]
>> count -= sizeof(*sl);
>> 282260: 91002063 add x3, x3, #0x8
>> 282264: 17fffff2 b 28222c <memset+0x20>
>> unsigned long *sl = (unsigned long *) s;
>> 282268: aa0003e3 mov x3, x0
>> 28226c: 17fffff8 b 28224c <memset+0x40>
>> *s8++ = c;
>> 282270: 38246861 strb w1, [x3, x4]
>> 282274: 91000484 add x4, x4, #0x1
>> 282278: 17fffff6 b 282250 <memset+0x44>
>>
>> 000000000028227c <memcpy>:
>> __used void * memcpy(void *dest, const void *src, size_t count)
>> {
>> unsigned long *dl = (unsigned long *)dest, *sl = (unsigned long *)src;
>> char *d8, *s8;
>>
>> if (src == dest)
>> 28227c: eb01001f cmp x0, x1
>> 282280: 54000100 b.eq 2822a0 <memcpy+0x24> // b.none
>> return dest;
>>
>> /* while all data is aligned (common case), copy a word at a time */
>> if ( (((ulong)dest | (ulong)src) & (sizeof(*dl) - 1)) == 0) {
>> 282284: aa010003 orr x3, x0, x1
>> 282288: f2400863 ands x3, x3, #0x7
>> 28228c: 54000120 b.eq 2822b0 <memcpy+0x34> // b.none
>> 282290: aa0003e4 mov x4, x0
>> 282294: d2800003 mov x3, #0x0 // #0
>> }
>> }
>> /* copy the reset one byte at a time */
>> d8 = (char *)dl;
>> s8 = (char *)sl;
>> while (count--)
>> 282298: eb03005f cmp x2, x3
>> 28229c: 540001e1 b.ne 2822d8 <memcpy+0x5c> // b.any
>> *d8++ = *s8++;
>>
>> return dest;
>> }
>> 2822a0: d65f03c0 ret
>> *dl++ = *sl++;
>> 2822a4: f8636824 ldr x4, [x1, x3]
>> 2822a8: f8236804 str x4, [x0, x3]
>> count -= sizeof(*dl);
>> 2822ac: 91002063 add x3, x3, #0x8
>> while (count >= sizeof(*dl)) {
>> 2822b0: cb030044 sub x4, x2, x3
>> 2822b4: f1001c9f cmp x4, #0x7
>> 2822b8: 54ffff68 b.hi 2822a4 <memcpy+0x28> // b.pmore
>> 2822bc: d343fc43 lsr x3, x2, #3
>> 2822c0: 928000e4 mov x4, #0xfffffffffffffff8 // #-8
>> 2822c4: 9b047c63 mul x3, x3, x4
>> 2822c8: 8b030042 add x2, x2, x3
>> 2822cc: cb030004 sub x4, x0, x3
>> 2822d0: cb030021 sub x1, x1, x3
>> 2822d4: 17fffff0 b 282294 <memcpy+0x18>
>> *d8++ = *s8++;
>> 2822d8: 38636825 ldrb w5, [x1, x3]
>> 2822dc: 38236885 strb w5, [x4, x3]
>> 2822e0: 91000463 add x3, x3, #0x1
>> 2822e4: 17ffffed b 282298 <memcpy+0x1c>
>>
>>
>> I tried enabling CONFIG_USE_ARCH_MEMCPY=y, CONFIG_USE_ARCH_MEMSET=y in
>> the .config (but leaving it disabled in SPL/TPL) and it results in
>> Synchronous Abort:
>> U-Boot SPL 2024.04 (Apr 02 2024 - 10:58:58 +0000)
>> Trying to boot from MMC1
>> NOTICE: BL31: v1.3(release):8f40012ab
>> NOTICE: BL31: Built : 14:20:53, Feb 16 2023
>> NOTICE: BL31: Rockchip release version: v1.1
>> INFO: GICv3 with legacy support detected. ARM GICV3 driver initialized in EL3
>> INFO: Using opteed sec cpu_context!
>> INFO: boot cpu mask: 0
>> INFO: plat_rockchip_pmu_init(1203): pd status 3e
>> INFO: BL31: Initializing runtime services
>> WARNING: No OPTEE provided by BL2 boot loader, Booting device without
>> OPTEE initialization. SMC`s destined for OPTEE will return SMC_UNK
>> ERROR: Error initializing runtime service opteed_fast
>> INFO: BL31: Preparing for EL3 exit to normal world
>> INFO: Entry point address = 0x200000
>> INFO: SPSR = 0x3c9
>> "Synchronous Abort" handler, esr 0x96000021, far 0x2957e1
>> elr: 000000000020233c lr : 000000000026a388
>> x0 : 00000000002fbf38 x1 : 00000000002957e1
>> x2 : 0000000000000008 x3 : 0000000000000065
>> x4 : 00000000002957e9 x5 : 00000000002fbf40
>> x6 : 0000000000000065 x7 : 0000000000000003
>> x8 : 00000000002c7960 x9 : 000000000000ffd0
>> x10: 00000000002fbc5c x11: 00000000000132e8
>> x12: 00000000002fbce8 x13: 00000000002c7960
>> x14: 00000000002c7960 x15: 0000000000000000
>> x16: 0000000000000000 x17: 0000000000000000
>> x18: 00000000002fbe30 x19: 0000000000000007
>> x20: 00000000002957d8 x21: 0000000000000009
>> x22: 000000000029d189 x23: 0000000000000020
>> x24: 00000000002fbf38 x25: 00000000002957e7
>> x26: 00000000002957b2 x27: 0000000000007fff
>> x28: 0000000000000000 x29: 00000000002fbcc0
>>
>> Code: a9001c06 a93f34ac d65f03c0 361800c2 (f9400026)
>> Resetting CPU ...
>>
>> resetting ...
>>
>> Thanks,
>> Gao Xiang
>>
>> Regards,
>> Jonathan