On Fri, Nov 12, 2010 at 8:41 AM, stephane eranian <eran...@googlemail.com>wrote:
> On Fri, Nov 12, 2010 at 2:22 PM, heechul Yun <heec...@illinois.edu> wrote:
> > 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;
> >
>
> Ok, I will post a file for this on LKML.
> Unless you want to do it.
>
>
It seems that it is already fixed in the latest 2.6.36 release. All pre
2.6.36 (2.6.35 - 2.6.32 at least) had the bug.
Heechul
> 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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> >
>
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