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问perf_event_open总是返回-1
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Stack Overflow用户

提问于 2016-07-18 17:37:52

回答 4查看 3.5K关注 0票数 6

我运行了以下程序，调用perf_event_open syscall : Linux -桌面3.18.0-20-rpi2 #21-UbuntuSMP抢占Sun 5 01:56:02 UTC 2015 UTC armv7l GNU/Linux

该方案：

#define _GNU_SOURCE 1

#include <asm/unistd.h>
#include <fcntl.h>
#include <linux/perf_event.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

long perf_event_open(struct perf_event_attr* event_attr, pid_t pid, int cpu, int group_fd, unsigned long flags)
{
    return syscall(__NR_perf_event_open, event_attr, pid, cpu, group_fd, flags);
}

static void perf_event_handler(int signum, siginfo_t* info, void* ucontext) {
    if(info->si_code != POLL_HUP) {
        // Only POLL_HUP should happen.
        exit(EXIT_FAILURE);
    }

    ioctl(info->si_fd, PERF_EVENT_IOC_REFRESH, 1);
}

int main(int argc, char** argv)
{
    // Configure signal handler
    struct sigaction sa;
    memset(&sa, 0, sizeof(struct sigaction));
    sa.sa_sigaction = perf_event_handler;
    sa.sa_flags = SA_SIGINFO;

    // Setup signal handler
    if (sigaction(SIGIO, &sa, NULL) < 0) {
        fprintf(stderr,"Error setting up signal handler\n");
        perror("sigaction");
        exit(EXIT_FAILURE);
    }

    // Configure perf_event_attr struct
    struct perf_event_attr pe;
    memset(&pe, 0, sizeof(struct perf_event_attr));
    pe.type = PERF_TYPE_HARDWARE;
    pe.size = sizeof(struct perf_event_attr);
    pe.config = PERF_COUNT_HW_INSTRUCTIONS;     // Count retired hardware instructions
    pe.disabled = 1;        // Event is initially disabled
    pe.sample_type = PERF_SAMPLE_IP;
    pe.sample_period = 1000;
    pe.exclude_kernel = 1;  // excluding events that happen in the kernel-space
    pe.exclude_hv = 1;      // excluding events that happen in the hypervisor

    pid_t pid = 0;  // measure the current process/thread
    int cpu = -1;   // measure on any cpu
    int group_fd = -1;
    unsigned long flags = 0;

    int fd = perf_event_open(&pe, pid, cpu, group_fd, flags);
    if (fd == -1) {
        fprintf(stderr, "Error opening leader %llx\n", pe.config);
        perror("perf_event_open");
        exit(EXIT_FAILURE);
    }
    // Setup event handler for overflow signals
    fcntl(fd, F_SETFL, O_NONBLOCK|O_ASYNC);
    fcntl(fd, F_SETSIG, SIGIO);
    fcntl(fd, F_SETOWN, getpid());

    ioctl(fd, PERF_EVENT_IOC_RESET, 0);     // Reset event counter to 0
    ioctl(fd, PERF_EVENT_IOC_REFRESH, 1);   // 

// Start monitoring

    long loopCount = 1000000;
    long c = 0;
    long i = 0;

    // Some sample payload.
    for(i = 0; i < loopCount; i++) {
        c += 1;
    }

// End monitoring

    ioctl(fd, PERF_EVENT_IOC_DISABLE, 0);   // Disable event

    long long counter;
    read(fd, &counter, sizeof(long long));  // Read event counter value

    printf("Used %lld instructions\n", counter);

    close(fd);
}

它返回错误的打开领导。我检查了fd，看起来它总是返回-1。

我使用了perf手册中的第二个例子，它有相同的问题(由fd=-1触发的错误打开领导者)。下面是手册中perf的示例代码：

  #include <stdlib.h>
   #include <stdio.h>
   #include <unistd.h>
   #include <string.h>
   #include <sys/ioctl.h>
   #include <linux/perf_event.h>
   #include <asm/unistd.h>

   static long
   perf_event_open(struct perf_event_attr *hw_event, pid_t pid,
                   int cpu, int group_fd, unsigned long flags)
   {
       int ret;

       ret = syscall(__NR_perf_event_open, hw_event, pid, cpu,
                      group_fd, flags);
       return ret;
   }

   int
   main(int argc, char **argv)
   {
       struct perf_event_attr pe;
       long long count;
       int fd;

       memset(&pe, 0, sizeof(struct perf_event_attr));
       pe.type = PERF_TYPE_HARDWARE;
       pe.size = sizeof(struct perf_event_attr);
       pe.config = PERF_COUNT_HW_INSTRUCTIONS;
       pe.disabled = 1;
       pe.exclude_kernel = 1;
       pe.exclude_hv = 1;

       fd = perf_event_open(&pe, 0, -1, -1, 0);
       if (fd == -1) {
          fprintf(stderr, "Error opening leader %llx\n", pe.config);
          exit(EXIT_FAILURE);
       }

       ioctl(fd, PERF_EVENT_IOC_RESET, 0);
       ioctl(fd, PERF_EVENT_IOC_ENABLE, 0);

       printf("Measuring instruction count for this printf\n");

       ioctl(fd, PERF_EVENT_IOC_DISABLE, 0);
       read(fd, &count, sizeof(long long));

       printf("Used %lld instructions\n", count);

       close(fd);
   }

我还编写了自己的代码，只检查perf在访问PMU寄存器时是否有问题。为此，我制作了一个内核模块，使用户模式访问PMU寄存器。

内核模式只执行以下操作：

    asm volatile("mrc p15, 0, %0, c9, c14, 0" :: "r"(1));
    asm volatile("mcr p15, 0, %0, c9, c14, 0" :: "r"(1));

然后我试着运行perf_event_open

init(void)
{
        static struct perf_event_attr attr;
        attr.type = PERF_TYPE_HARDWARE;
//      attr.config = PERF_COUNT_HW_INSTRUCTIONS;
        attr.config = PERF_COUNT_HW_CPU_CYCLES;
        fddev = syscall(__NR_perf_event_open, &attr, 0, -1, -1, 0);
        printf("The fddev value is %d", fddev);
}

返回-1。我还使用了这个回购，它再次返回fd -1。

我还查看了kallsym，以确保perf_event_open的syscall在那里。

root@sama-desktop:/home/sama# cat /proc/kallsyms | grep "perf_event_open"
800f3178 T SyS_perf_event_open
800f3178 T sys_perf_event_open

下面是/boot/config-3.18.0-20-rpi2的输出：

# 
# Kernel Performance Events And Counters
#
CONFIG_PERF_EVENTS=y
# CONFIG_DEBUG_PERF_USE_VMALLOC is not set
CONFIG_VM_EVENT_COUNTERS=y
# CONFIG_COMPAT_BRK is not set
CONFIG_SLAB=y
# CONFIG_SLUB is not set
# CONFIG_SLOB is not set
# CONFIG_SYSTEM_TRUSTED_KEYRING is not set
CONFIG_PROFILING=y
CONFIG_TRACEPOINTS=y
CONFIG_OPROFILE=m
CONFIG_HAVE_OPROFILE=y
CONFIG_KPROBES=y
CONFIG_JUMP_LABEL=y
CONFIG_UPROBES=y
# CONFIG_HAVE_64BIT_ALIGNED_ACCESS is not set
CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS=y
CONFIG_ARCH_USE_BUILTIN_BSWAP=y
CONFIG_KRETPROBES=y
CONFIG_HAVE_KPROBES=y
CONFIG_HAVE_KRETPROBES=y
CONFIG_HAVE_ARCH_TRACEHOOK=y
CONFIG_HAVE_DMA_ATTRS=y
CONFIG_HAVE_DMA_CONTIGUOUS=y
CONFIG_GENERIC_SMP_IDLE_THREAD=y
CONFIG_GENERIC_IDLE_POLL_SETUP=y
CONFIG_HAVE_REGS_AND_STACK_ACCESS_API=y
CONFIG_HAVE_CLK=y
CONFIG_HAVE_DMA_API_DEBUG=y
CONFIG_HAVE_HW_BREAKPOINT=y
CONFIG_HAVE_PERF_REGS=y
CONFIG_HAVE_PERF_USER_STACK_DUMP=y
CONFIG_HAVE_ARCH_JUMP_LABEL=y
CONFIG_ARCH_WANT_IPC_PARSE_VERSION=y
CONFIG_HAVE_ARCH_SECCOMP_FILTER=y
CONFIG_SECCOMP_FILTER=y
CONFIG_HAVE_CC_STACKPROTECTOR=y
CONFIG_CC_STACKPROTECTOR=y
# CONFIG_CC_STACKPROTECTOR_NONE is not set
CONFIG_CC_STACKPROTECTOR_REGULAR=y
# CONFIG_CC_STACKPROTECTOR_STRONG is not set
CONFIG_HAVE_CONTEXT_TRACKING=y
CONFIG_HAVE_VIRT_CPU_ACCOUNTING_GEN=y
CONFIG_HAVE_IRQ_TIME_ACCOUNTING=y
CONFIG_HAVE_MOD_ARCH_SPECIFIC=y
CONFIG_MODULES_USE_ELF_REL=y
CONFIG_CLONE_BACKWARDS=y
CONFIG_OLD_SIGSUSPEND3=y
CONFIG_OLD_SIGACTION=y

下面是dmesg的输出：

root@sama-desktop:/boot# dmesg | grep "perf"
[    0.003891] Initializing cgroup subsys perf_event

下面是设备树的输出：

root@sama-desktop:# ls -la /sys/bus/event_source/devices
total 0
drwxr-xr-x 2 root root 0 jul 18 20:15 .
drwxr-xr-x 4 root root 0 jan  1  1970 ..
lrwxrwxrwx 1 root root 0 jan  1  1970 breakpoint -> ../../../devices/breakpoint
lrwxrwxrwx 1 root root 0 jan  1  1970 software -> ../../../devices/software
lrwxrwxrwx 1 root root 0 jan  1  1970 tracepoint -> ../../../devices/tracepoint

我真的不知道为什么perf_event_open返回-1。

linux

arm

system-calls

perf

回答 4

Stack Overflow用户

回答已采纳

发布于 2016-07-18 21:14:56

由于缺乏dmesg和sysfs中的相关内容，希望现在应该可以看出，PMU并没有被描述给内核。因此perf事件对您所要求的硬件事件一无所知，因此没有打开它也就不足为奇了。您需要做的是确保内核确实了解PMU，这样驱动程序就应该通过CONFIG_HW_PERF_EVENTS (默认情况下与CONFIG_PERF_EVENTS一起打开，并且在配置中看起来不会被禁用)来获取它--说到驱动程序应该已经内置了，但是它可能值得一次检查。

它看起来像在其3.18内核中的devicetree描述，所以我最好的猜测是，您的董事会可能使用的是旧板文件，而不是FDT。我不太了解Raspberry的具体内容，但从这篇相当详尽的文章 (我可以说直接跳到3.1节)判断，重新配置引导加载程序使用FDT似乎相对简单。

票数 1

Stack Overflow用户

发布于 2017-05-28 22:01:01

对于任何使用Yocto i.MX6构建来回答这个问题的人，比如我的，但与OP不同的是，在dmesg中确实有这样的东西：

hw perfevents: enabled with armv7_cortex_a9 PMU driver, 7 counters available

试着在示例代码中注释掉这两行：

pe.exclude_kernel = 1;
pe.exclude_hv = 1;

对我来说，这使得perf_event_open调用成功，我能够收集数据。

票数 1

Stack Overflow用户

发布于 2017-12-02 13:09:32

我刚才和你有同样的问题，现在我的问题是程序的许可，你应该使用更高的权限来运行它，这样一切都是正确的。我使用sudo ./a.out，然后一切都是fine.Maybe --这将有所帮助。

票数 0

页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持

原文链接：

https://stackoverflow.com/questions/38442839

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