这有点棘手。
我们像往常一样创建第一个计数器。另外,我们通过PERF_FORMAT_GROUP
and PERF_FORMAT_ID
能够同时与多个计数器一起工作。这个柜台将是我们的组长。
struct perf_event_attr pea;
int fd1, fd2;
uint64_t id1, id2;
memset(&pea, 0, sizeof(struct perf_event_attr));
pea.type = PERF_TYPE_HARDWARE;
pea.size = sizeof(struct perf_event_attr);
pea.config = PERF_COUNT_HW_CPU_CYCLES;
pea.disabled = 1;
pea.exclude_kernel = 1;
pea.exclude_hv = 1;
pea.read_format = PERF_FORMAT_GROUP | PERF_FORMAT_ID;
fd1 = syscall(__NR_perf_event_open, &pea, 0, -1, -1, 0);
接下来,我们检索第一个计数器的标识符:
ioctl(fd1, PERF_EVENT_IOC_ID, &id1);
第二个(以及所有其他计数器)以相同的方式创建,只有一个例外:我们通过fd1
作为小组领导者的价值论点:
memset(&pea, 0, sizeof(struct perf_event_attr));
pea.type = PERF_TYPE_SOFTWARE;
pea.size = sizeof(struct perf_event_attr);
pea.config = PERF_COUNT_SW_PAGE_FAULTS;
pea.disabled = 1;
pea.exclude_kernel = 1;
pea.exclude_hv = 1;
pea.read_format = PERF_FORMAT_GROUP | PERF_FORMAT_ID;
fd2 = syscall(__NR_perf_event_open, &pea, 0, -1, fd1, 0); // <-- here
ioctl(fd2, PERF_EVENT_IOC_ID, &id2);
接下来我们需要声明一个数据结构来一次读取多个计数器。您必须根据传递给的标志声明不同的字段集perf_event_open
。手册页提到了所有可能的字段。在我们的例子中,我们通过了PERF_FORMAT_ID
添加的标志id
场地。这将使我们能够区分不同的计数器。
struct read_format {
uint64_t nr;
struct {
uint64_t value;
uint64_t id;
} values[/*2*/];
};
现在我们调用标准分析 ioctl:
ioctl(fd1, PERF_EVENT_IOC_RESET, PERF_IOC_FLAG_GROUP);
ioctl(fd1, PERF_EVENT_IOC_ENABLE, PERF_IOC_FLAG_GROUP);
do_something();
ioctl(fd1, PERF_EVENT_IOC_DISABLE, PERF_IOC_FLAG_GROUP);
最后,我们从组领导文件描述符中读取计数器。两个计数器均以单个形式返回read_format
我们声明的结构:
char buf[4096];
struct read_format* rf = (struct read_format*) buf;
uint64_t val1, val2;
read(fd1, buf, sizeof(buf));
for (i = 0; i < rf->nr; i++) {
if (rf->values[i].id == id1) {
val1 = rf->values[i].value;
} else if (rf->values[i].id == id2) {
val2 = rf->values[i].value;
}
}
printf("cpu cycles: %"PRIu64"\n", val1);
printf("page faults: %"PRIu64"\n", val2);
以下是完整的程序清单:
#define _GNU_SOURCE
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/syscall.h>
#include <string.h>
#include <sys/ioctl.h>
#include <linux/perf_event.h>
#include <linux/hw_breakpoint.h>
#include <asm/unistd.h>
#include <errno.h>
#include <stdint.h>
#include <inttypes.h>
struct read_format {
uint64_t nr;
struct {
uint64_t value;
uint64_t id;
} values[];
};
void do_something() {
int i;
char* ptr;
ptr = malloc(100*1024*1024);
for (i = 0; i < 100*1024*1024; i++) {
ptr[i] = (char) (i & 0xff); // pagefault
}
free(ptr);
}
int main(int argc, char* argv[]) {
struct perf_event_attr pea;
int fd1, fd2;
uint64_t id1, id2;
uint64_t val1, val2;
char buf[4096];
struct read_format* rf = (struct read_format*) buf;
int i;
memset(&pea, 0, sizeof(struct perf_event_attr));
pea.type = PERF_TYPE_HARDWARE;
pea.size = sizeof(struct perf_event_attr);
pea.config = PERF_COUNT_HW_CPU_CYCLES;
pea.disabled = 1;
pea.exclude_kernel = 1;
pea.exclude_hv = 1;
pea.read_format = PERF_FORMAT_GROUP | PERF_FORMAT_ID;
fd1 = syscall(__NR_perf_event_open, &pea, 0, -1, -1, 0);
ioctl(fd1, PERF_EVENT_IOC_ID, &id1);
memset(&pea, 0, sizeof(struct perf_event_attr));
pea.type = PERF_TYPE_SOFTWARE;
pea.size = sizeof(struct perf_event_attr);
pea.config = PERF_COUNT_SW_PAGE_FAULTS;
pea.disabled = 1;
pea.exclude_kernel = 1;
pea.exclude_hv = 1;
pea.read_format = PERF_FORMAT_GROUP | PERF_FORMAT_ID;
fd2 = syscall(__NR_perf_event_open, &pea, 0, -1, fd1 /*!!!*/, 0);
ioctl(fd2, PERF_EVENT_IOC_ID, &id2);
ioctl(fd1, PERF_EVENT_IOC_RESET, PERF_IOC_FLAG_GROUP);
ioctl(fd1, PERF_EVENT_IOC_ENABLE, PERF_IOC_FLAG_GROUP);
do_something();
ioctl(fd1, PERF_EVENT_IOC_DISABLE, PERF_IOC_FLAG_GROUP);
read(fd1, buf, sizeof(buf));
for (i = 0; i < rf->nr; i++) {
if (rf->values[i].id == id1) {
val1 = rf->values[i].value;
} else if (rf->values[i].id == id2) {
val2 = rf->values[i].value;
}
}
printf("cpu cycles: %"PRIu64"\n", val1);
printf("page faults: %"PRIu64"\n", val2);
return 0;
}