Re: [PATCH RFC] x86: avoid atomic operation in test_and_set_bit_lock if possible

Ingo Molnar
2011-03-24T20:54:58Z

* Eric Dumazet <eric.dumazet@gmail.com> wrote:

> Le jeudi 24 mars 2011 à 21:00 +0100, Ingo Molnar a écrit :
>
> > One good way to see cache bounces is to run a misses/accesses ratio profile:
> >
> > perf top -e cache-misses -e cache-references --count-filter 10
> >
>
> Oh well , something must be broken...
>
> "perf top" is working here, but if I use any "-e ...." argument, it
> fails :
>
> # perf top -e cache-misses
>
> Error: sys_perf_event_open() syscall returned with 2 (No such file or directory).
> /bin/dmesg may provide additional information.
>
> Fatal: No CONFIG_PERF_EVENTS=y kernel support configured?
>
> # grep PERF_EVENTS .config
> CONFIG_HAVE_PERF_EVENTS=y
> CONFIG_PERF_EVENTS=y
> CONFIG_HAVE_PERF_EVENTS_NMI=y
>
> Nothing in dmesg...
>
> uname -a
> Linux ed001 2.6.38-08165-g2712750-dirty #517 SMP Thu Mar 24 21:31:00 CET 2011 i686 i686 i386 GNU/Linux

Does it work better if you run it as root?

To easiest way to debug as user is to do:

echo -1 > /proc/sys/kernel/perf_event_paranoid

and to put this into /etc/sysctl.conf:

kernel.perf_event_paranoid = -1

Thanks,

Ingo