It was because of a bug in kernel/perf_event.c as shown in the following.
static int perf_event_period(struct perf_event *event, u64 __user *arg)
{
...
size = copy_from_user(&value, arg, sizeof(value));
if (size != sizeof(value)) *// <--------- bug. should be: if (!size)
return -EFAULT *
return -EFAULT;
I found this bug has been there in all versions before it was finally fixed
in 2.6.36.
Heechul
On Thu, Nov 11, 2010 at 9:23 PM, heechul Yun <heec...@illinois.edu> wrote:
> Hi,
>
> I wanted to adjust sampling period using PERF_EVENT_IOC_PERIOD ioctl.
> I modified the notify_group to change the period at runtime as follows.
>
> diff --git a/perf_examples/notify_group.c b/perf_examples/notify_group.c
> index 76869b0..d8ff5e1 100644
> --- a/perf_examples/notify_group.c
> +++ b/perf_examples/notify_group.c
> @@ -54,6 +54,7 @@ sigio_handler(int n, struct siginfo *info, struct
> sigcontext *sc)
> struct perf_event_mmap_page *hdr;
> struct perf_event_header ehdr;
> uint64_t ip;
> + uint64_t new_period;
> int id, ret;
>
> id = perf_fd2event(fds, num_fds, info->si_fd);
> @@ -87,6 +88,11 @@ skip:
> /*
> * rearm the counter for one more shot
> */
> + new_period = SMPL_PERIOD * 2 ;
> + ret = ioctl(info->si_fd, PERF_EVENT_IOC_PERIOD, new_period);
> + if (ret == -1)
> + err(1, "cannot set");
> +
> ret = ioctl(info->si_fd, PERF_EVENT_IOC_REFRESH, 1);
> if (ret == -1)
> err(1, "cannot refresh");
>
> It, however, failed to do so as belows.
>
> $ ./notify_group
> i=0 disabled=0
> i=1 disabled=1
> i=2 disabled=1
> Notification 1: 0x8048f63 fd=3 PERF_COUNT_HW_CPU_CYCLES
> notify_group: cannot set: Invalid argument
>
> Any idea?
>
>
> BTW, I found an error in perf_event.h of libpfm4 which prevents compiling
> the code.
> The following diff is the fix.
>
> diff --git a/include/perfmon/perf_event.h b/include/perfmon/perf_event.h
> index cfddef0..7f2889e 100644
> --- a/include/perfmon/perf_event.h
> +++ b/include/perfmon/perf_event.h
> @@ -13,7 +13,7 @@
> */
> #ifndef _LINUX_PERF_EVENT_H
> #define _LINUX_PERF_EVENT_H
> -
> +#include <linux/types.h>
> #include <sys/types.h>
> #include <inttypes.h>
> #ifndef PR_TASK_PERF_EVENTS_DISABLE
> @@ -236,7 +236,7 @@ typedef struct perf_event_attr {
> #define PERF_EVENT_IOC_DISABLE _IO ('$', 1)
> #define PERF_EVENT_IOC_REFRESH _IO ('$', 2)
> #define PERF_EVENT_IOC_RESET _IO ('$', 3)
> -#define PERF_EVENT_IOC_PERIOD _IOW('$', 4, u64)
> +#define PERF_EVENT_IOC_PERIOD _IOW('$', 4, __u64)
> #define PERF_EVENT_IOC_SET_OUTPUT _IO ('$', 5)
> #define PERF_EVENT_IOC_SET_FILTER _IOW('$', 6, char *)
>
>
> - Heechul
>
>
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