It seems that still there's a problem. The problem is the changed period,
using ioctl(fd, PERF_EVENT_IOC_PERIOD, &new), does not takes effect on the
next overflow but on the next next overflow.
What I did is as follows: on every overflow (1) print the current counter
value, and (2) set the new sampling period (=previous sampling period +
10000000) and rearm it.
With initial sample_period = 10000000ULL, the expected behavior was
something like the below.
1 | value = 10000000 | new_period = 20000000
2 | value = 30000000 | new_period = 30000000
3 | value = 60000000 | new_period = 40000000
4 | value = 100000000 | new_period = 50000000
5 | value = 150000000 | new_period = 60000000
The actual was, however, as follows:
1 | value = 10000000 | new_period = 20000000
2 | value = 20000000 | new_period = 30000000
3 | value = 40000000 | new_period = 40000000
4 | value = 70000000 | new_period = 50000000
5 | value = 110000000 | new_period = 60000000
As you can see, the first ioctl, new_period=20000000, took effect on 3rd
signal not the 2nd signal handling. Likewise, the second ioctl,
new_period=30000000, took effect on 4th signal handling.
Is this expected behavior? if not, how can this be corrected?
The code I used is slightly modified notify_group.c of libpfm4 as shown in
the following.
--< notify_group.c >--
#define SMPL_PERIOD 10000000ULL
static void
sigio_handler(int n, struct siginfo *info, struct sigcontext *sc)
{
...
notification_received++;
read(info->si_fd, values, sizeof(values));
printf("%d | value = %lld | new_period = %lld\n", notification_received,
values[0], new_period);
new_period = SMPL_PERIOD * (notification_received + 1);
ret = ioctl(info->si_fd, PERF_EVENT_IOC_PERIOD, &new_period);
ret = ioctl(info->si_fd, PERF_EVENT_IOC_REFRESH, 1);
}
On Fri, Nov 12, 2010 at 9:40 AM, stephane eranian <eran...@googlemail.com>wrote:
> On Fri, Nov 12, 2010 at 4:36 PM, heechul Yun <heec...@illinois.edu> wrote:
> >
> >
> > 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.
>
> That sounds familiar. Yes, now I remember seeing a fix about
> copy_from_user().
> Thanks for tracking this down on your side anyway.
>
>
> > 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
> >> >
> >> >
> >> >
> >> >
> ------------------------------------------------------------------------------
> >> > Centralized Desktop Delivery: Dell and VMware Reference Architecture
> >> > Simplifying enterprise desktop deployment and management using
> >> > Dell EqualLogic storage and VMware View: A highly scalable, end-to-end
> >> > client virtualization framework. Read more!
> >> > http://p.sf.net/sfu/dell-eql-dev2dev
> >> > _______________________________________________
> >> > perfmon2-devel mailing list
> >> > perfmon2-devel@lists.sourceforge.net
> >> > https://lists.sourceforge.net/lists/listinfo/perfmon2-devel
> >> >
> >> >
> >
> >
>
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Simplifying enterprise desktop deployment and management using
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