Re: [PATCH 2/3] x86/hash: swap parameters of crc32_u32()
From: Daniel Borkmann
Date: Mon Feb 24 2014 - 05:22:56 EST
On 02/24/2014 09:03 AM, Jan Beulich wrote:
On 22.02.14 at 13:09, Daniel Borkmann <dborkman@xxxxxxxxxx> wrote:
On 02/21/2014 11:33 AM, Jan Beulich wrote:
... to match its two callers (i.e. the alternative would have been to
swap the arguments at the call sites).
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Francesco Fusco <ffusco@xxxxxxxxxx>
Cc: Daniel Borkmann <dborkman@xxxxxxxxxx>
Cc: Thomas Graf <tgraf@xxxxxxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
---
arch/x86/lib/hash.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- 3.14-rc3-x86-hash-crc32.orig/arch/x86/lib/hash.c
+++ 3.14-rc3-x86-hash-crc32/arch/x86/lib/hash.c
@@ -37,7 +37,7 @@
#include <asm/cpufeature.h>
#include <asm/hash.h>
-static inline u32 crc32_u32(u32 crc, u32 val)
+static inline u32 crc32_u32(u32 val, u32 crc)
{
#ifdef CONFIG_AS_CRC32
asm ("crc32l %1,%0\n" : "+r" (crc) : "rm" (val));
Can you elaborate?
Sorry, I need to ask here (even if it's a stupid question ;)) if this
change is safe to do; are referring to a cleanup or fixing a concrete
bug? The code is a modified version of the DPDK hash which you can find
in [1]. Arguments of the caller are in the correct order, afaik.
[1] http://dpdk.org/browse/dpdk/tree/lib/librte_hash/rte_hash_crc.h
Yes, that file appears to be correct:
rte_hash_crc_4byte(uint32_t data, uint32_t init_val)
as opposed to
static inline u32 crc32_u32(u32 crc, u32 val)
(quite obviously data <-> val and crc <-> init_val, supported
by the second argument in each caller being named "seed").
If you want a more descriptive name, feel free to rename these vars,
but check it yourself, it's not a bug as you claim; results are the
same:
/* gcc -march=corei7 -Wall -O2 intel_crc.c -lgsl
* ./a.out
* Result: good:10000 bad:0
*/
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <nmmintrin.h>
#include <gsl/gsl_rng.h>
/* Kernel code */
static inline uint32_t crc32_u32(uint32_t crc, uint32_t val)
{
asm ("crc32l %1,%0\n" : "+r" (crc) : "rm" (val));
return crc;
}
static uint32_t intel_crc4_2_hash(const void *data, uint32_t len, uint32_t seed)
{
const uint32_t *p32 = (const uint32_t *) data;
uint32_t i;
for (i = 0; i < len / 4; i++)
seed = crc32_u32(*p32++, seed);
return seed;
}
/* DPDK code */
static inline uint32_t rte_hash_crc_4byte(uint32_t data, uint32_t init_val)
{
return _mm_crc32_u32(data, init_val);
}
static inline uint32_t rte_hash_crc(const void *data, uint32_t data_len,
uint32_t init_val)
{
const uint32_t *p32 = (const uint32_t *) data;
unsigned i;
for (i = 0; i < data_len / 4; i++)
init_val = rte_hash_crc_4byte(*p32++, init_val);
return init_val;
}
/* Test case */
static void fill_foo(gsl_rng *rng, void *foo, size_t len)
{
uint32_t *foo_32 = foo;
int i;
for (i = 0; i < len; i += sizeof(uint32_t))
foo_32[i] = gsl_rng_get(rng);
}
int main(void)
{
int i, good = 0, bad = 0;
gsl_rng *rng;
srand(time(NULL));
gsl_rng_default_seed = rand();
rng = gsl_rng_alloc(gsl_rng_taus113);
if (rng == NULL)
return -1;
for (i = 0; i < 10000; i++) {
char foo[sizeof(uint32_t) * 128];
uint32_t val1, val2, seed = gsl_rng_get(rng);
fill_foo(rng, foo, sizeof(foo));
val1 = rte_hash_crc(foo, sizeof(foo), seed);
val2 = intel_crc4_2_hash(foo, sizeof(foo), seed);
if (val1 != val2)
bad++;
else
good++;
}
gsl_rng_free(rng);
printf("Result: good:%d bad:%d\n", good, bad);
return 0;
}
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