Hi Kirill,
On 7/13/07, Kirill Korotaev <[EMAIL PROTECTED]> wrote:
Look, until you have any numbers in hands it's impossible to say
which one is faster.
Well, it's not too hard to guess: struct dentry is 124 bytes on i386
so kmem_cache_zalloc over it is bound to be slower tha
kmem_cache_alloc as most members are initialized to non-NULL. And if
you're into micro-benchmarks, here's one:
d_alloc takes 182.75ns
d_alloc_zalloc takes 315.89ns
So definitely NAK for Denis' patch.
Pekka
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <string.h>
#include <time.h>
struct dentry {
void *a;
void *b;
void *c;
void *d;
void *e;
void *f;
void *g;
void *h;
unsigned char d_iname[36];
};
#define NR_ITERS 1000000
#define MAX_DENTRIES (NR_ITERS*2)
static unsigned long offset;
static struct dentry dentries[MAX_DENTRIES];
static inline void *__kmalloc(void)
{
void *p = &dentries[offset++];
if (offset == MAX_DENTRIES)
offset = 0;
return p;
}
void *kmalloc(size_t sz)
{
return __kmalloc();
}
struct dentry *d_alloc(const char *name)
{
struct dentry *ret = kmalloc(sizeof *ret);
if (ret) {
ret->a = NULL;
ret->b = NULL;
ret->c = NULL;
ret->d = NULL;
ret->e = (void *) 0xdeadbeef;
ret->f = (void *) 0xdeadbeef;
ret->g = (void *) 0xdeadbeef;
ret->h = (void *) 0xdeadbeef;
strcpy(ret->d_iname, name);
}
return ret;
}
static inline void * __memset_generic(void * s, char c,size_t count)
{
int d0, d1;
__asm__ __volatile__(
"rep\n\t"
"stosb"
: "=&c" (d0), "=&D" (d1)
:"a" (c),"1" (s),"0" (count)
:"memory");
return s;
}
void *kzalloc(size_t sz)
{
void *p = __kmalloc();
if (p)
__memset_generic(p, 0, sz);
return p;
}
struct dentry *d_alloc_zalloc(const char *name)
{
struct dentry *ret = kzalloc(sizeof *ret);
if (ret) {
ret->e = (void *) 0xdeadbeef;
ret->f = (void *) 0xdeadbeef;
ret->g = (void *) 0xdeadbeef;
ret->h = (void *) 0xdeadbeef;
strcpy(ret->d_iname, name);
}
return ret;
}
int main(int argc, char *argv[])
{
struct timeval start, end;
unsigned long long usec;
int i;
gettimeofday(&start, NULL);
for (i = 0; i < NR_ITERS; i++) {
struct dentry *dentry = d_alloc("root");
if (!dentry || dentry->a != NULL)
abort();
}
gettimeofday(&end, NULL);
usec = end.tv_usec + 1000000*(end.tv_sec - start.tv_sec) -
start.tv_usec;
printf("d_alloc takes %0.2lfns\n", (double)usec * 1000 / NR_ITERS);
gettimeofday(&start, NULL);
for (i = 0; i < NR_ITERS; i++) {
struct dentry *dentry = d_alloc_zalloc("root");
if (!dentry || dentry->a != NULL)
abort();
}
gettimeofday(&end, NULL);
usec = end.tv_usec + 1000000*(end.tv_sec - start.tv_sec) -
start.tv_usec;
printf("d_alloc_zalloc takes %0.2lfns\n", (double)usec * 1000 /
NR_ITERS);
return 0;
}
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