RE: Optimize Arm64 crc32c implementation in Postgresql

Hi,

Thanks for all your comments.

> Could you show whether it actually improves performance? Usually bulk loading data with parallel COPYs is a good way to hit this code path.

The mini benchmark code:

#include <string.h>

#include <stdlib.h>

#include <stdint.h>

#include <sys/time.h>

#include "port/pg_crc32c.h"

long int GetTickCount() {

struct timeval tv;

gettimeofday(&tv, NULL);

return tv.tv_sec * 1000000 + tv.tv_usec;

}

int main() {

static const uint64_t kSize = 1024 * 1024 + 29;

uint8_t* buf = (uint8_t *)malloc(sizeof(uint8_t) * kSize);

uint32_t i;

srand(0);

for (i = 0; i < kSize; i++) {

buf[i] = (uint8_t)(rand() % 256u);

}

uint32_t kLoop = 1024;

long int start, end;

uint32_t crc = 0xFFFFFFFF;

start = GetTickCount();

for (i = 0; i < kLoop; i++) {

COMP_CRC32C(crc, buf, kSize);

}

end = GetTickCount();

crc ^= 0xFFFFFFFF;

if (kSize < 20) {

for (i = 0; i < kSize; i++) {

printf("%3u,", (uint32_t)buf[i]);

}

printf("\n");

}

printf("crc result = %x, time cost per loop:%f ms\n", crc, (double)(end - start) / kLoop);

free(buf);

return 0;

}

The result shows that optimization get x4.5 speedups on Cortex-A72.

> What's the availability of these headers and functions on non-linux platforms?

This Arm64 optimization code only supports linux os so far.

>asm(".arch_extension crc");

>#define CRC32CB(crc,value) asm("crc32cb %w[c], %w[c], %w[v]" : [c]"+r"(*&crc) : [v]"r"(+value))

It just adds crc flag for Arm gnu gcc compiler.

'crc32cb' might not be recognized in windows or xxxBSD.

So, is it reasonable to add an OS check for Arm64 crc32 optimization.

It means the application calls Arm64 crc32 interface only in linux based OS.

> From the department of trivialities, our coding style has braces like this:

>

> if (length & sizeof(uint16))

> {

> CRC32CH(crc32_c, *(uint16*)p_buf);

> p_buf += sizeof(uint16);

> }

> if (length & sizeof(uint8))

> CRC32CB(crc32_c, *p_buf);

Got it. I'll modify it.

> + --runstatedir=DIR modifiable per-process data [LOCALSTATEDIR/run]

>

> What is this for?

>Those probably are damage from using a distribution autoconf rather than stock autoconf.

What does it mean "stock autoconf" ?

Should the configure script be made by specific version autoconf ?

Thanks!

BRs,

Yuqi

-----Original Message-----
From: Andres Freund [mailto:andres(at)anarazel(dot)de]
Sent: Friday, March 2, 2018 5:36 AM
To: Yuqi Gu <Yuqi(dot)Gu(at)arm(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Optimize Arm64 crc32c implementation in Postgresql

Hi,

On 2018-01-10 05:58:19 +0000, Yuqi Gu wrote:

> Currently PostgreSQL only implements hardware support for CRC32 checksums for the x86_64 architecture.

> Some ARMv8 (AArch64) CPUs implement the CRC32 extension which is

> implemented by inline assembly, so they can also benefit from hardware acceleration in IO-intensive workloads.

>

> I would like to propose the patch to optimize crc32c calculation with Arm64 specific instructions.

> The hardware-specific code implementation is used under #if defined USE_ARMCE_CRC32C_WITH_RUNTIME_CHECK.

> And the performance is improved on platforms: cortex-A57, cortex-A72, cortex-A73, etc.

>

> I'll create a CommitFests ticket for this submission.

> Any comments or feedback are welcome.

Could you show whether it actually improves performance? Usually bulk loading data with parallel COPYs is a good way to hit this codepath.

> +

> +AC_DEFUN([PGAC_ARM64CE_CRC32_INTRINSICS],

> +[AC_CACHE_CHECK([for Arm64ce CRC32],

> +[pgac_cv_arm64ce_crc32_intrinsics],

> +[AC_LINK_IFELSE([AC_LANG_PROGRAM([],

> + [unsigned int arm_flag = 0;

> +#if defined(__ARM_ARCH) && (__ARM_ARCH > 7)

> + arm_flag = 1;

> +#endif

> + return arm_flag == 1;])],

> + [pgac_cv_arm64ce_crc32_intrinsics="yes"],

> + [pgac_cv_arm64ce_crc32_intrinsics="no"])])

> +if test x"$pgac_cv_arm64ce_crc32_intrinsics" = x"yes"; then

> + pgac_arm64ce_crc32_intrinsics=yes

> +fi

> +])# PGAC_ARM64CE_CRC32_INTRINSICS

I don't understand what this check is supposed to be doing?

AC_LINK_IFELSE doesn't run the program, so I don't see this test achieving anything at all?

> * Use slicing-by-8 algorithm.

> diff --git a/src/port/pg_crc32c_choose.c b/src/port/pg_crc32c_choose.c

> index 40bee67..d3682ad 100644

> --- a/src/port/pg_crc32c_choose.c

> +++ b/src/port/pg_crc32c_choose.c

> @@ -29,6 +29,20 @@

>

> #include "port/pg_crc32c.h"

>

> +#ifdef USE_ARMCE_CRC32C_WITH_RUNTIME_CHECK

> +#include <sys/auxv.h>

> +#include <asm/hwcap.h>

> +#ifndef HWCAP_CRC32

> +#define HWCAP_CRC32 (1 << 7)

> +#endif

> +static bool

> +pg_crc32c_arm64ce_available(void) {

> + unsigned long auxv = getauxval(AT_HWCAP);

> + return (auxv & HWCAP_CRC32) != 0;

> +}

> +

> +#else

What's the availability of these headers and functions on non-linux platforms?

> +#if defined(USE_ARMCE_CRC32C_WITH_RUNTIME_CHECK)

> +asm(".arch_extension crc");

So this emitted globally?

> +#define LDP(x,y,p) asm("ldp %x[a], %x[b], [%x[c]], #16" :

> +[a]"=r"(x),[b]"=r"(y),[c]"+r"(p))

> +/* CRC32C: Castagnoli polynomial 0x1EDC6F41 */ #define

> +CRC32CX(crc,value) asm("crc32cx %w[c], %w[c], %x[v]" : [c]"+r"(*&crc)

> +: [v]"r"(+value)) #define CRC32CW(crc,value) asm("crc32cw %w[c],

> +%w[c], %w[v]" : [c]"+r"(*&crc) : [v]"r"(+value)) #define

> +CRC32CH(crc,value) asm("crc32ch %w[c], %w[c], %w[v]" : [c]"+r"(*&crc)

> +: [v]"r"(+value)) #define CRC32CB(crc,value) asm("crc32cb %w[c],

> +%w[c], %w[v]" : [c]"+r"(*&crc) : [v]"r"(+value))

> +

> +pg_crc32c

> +pg_comp_crc32c_arm64(pg_crc32c crc, const void* data, size_t len) {

> + uint64 p0, p1;

> + pg_crc32c crc32_c = crc;

> + long length = len;

> + const unsigned char *p_buf = data;

> +

> + /* Allow crc instructions in asm */

> + asm(".cpu generic+crc");

Hm, this switches it for the rest of the function, program, ...?

Greetings,

Andres Freund

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