linux-kernel - Re: Performance Events hangs with Intel P4 system

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Date:	Fri, 14 May 2010 21:52:28 +0530
From:	Jaswinder Singh Rajput <jaswinderlinux@...il.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Lin Ming <ming.m.lin@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: Performance Events hangs with Intel P4 system

Hello Cyrill,

On Fri, May 14, 2010 at 8:22 PM, Cyrill Gorcunov <gorcunov@...il.com> wrote:
> [PATCH -tip/master] x86,perf: P4 PMU - fix counters allocation logic and sign issue
>
> Jaswinder reported GP:
> |
> | Message from syslogd@ht at May 14 09:39:32 ...
> | kernel:[  314.908612] EIP: [<c100ccca>]
> | x86_perf_event_set_period+0x19d/0x1b2 SS:ESP 0068:edac3d70
> |
>
> Ming has narrowed it down to comparision issue between arguments with
> different sizes. As result event index reaches value 255 which in turn
> leads to GP fault.
>
> Also it was found that p4_next_cntr has a broken logic and should return
> counter index if only it was not yet borrowed for another event.
>
> Reported-by: Jaswinder Singh Rajput <jaswinderlinux@...il.com>
> Reported-by: Lin Ming <ming.m.lin@...el.com>
> Bisected-by: Lin Ming <ming.m.lin@...el.com>
> CC: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> CC: Ingo Molnar <mingo@...e.hu>
> CC: Frederic Weisbecker <fweisbec@...il.com>
> Signed-off-by: Cyrill Gorcunov <gorcunov@...nvz.org>
> ---

Yes, this works for me. Now I am not getting general protection fault.

It seems hardware events are not supported for P4 yet.

$ ./perf stat -e
cycles,instructions,cache-references,cache-misses,branches,branch-misses,bus-cycles
ls > /dev/null

 Performance counter stats for 'ls':

  <not counted>  cycles
         601636  instructions             #      0.000 IPC    (scaled
from 91.80%)
  <not counted>  cache-references
  <not counted>  cache-misses
  <not counted>  branches
  <not counted>  branch-misses
  <not counted>  bus-cycles

    0.003364910  seconds time elapsed


Thanks,
--
Jaswinder Singh.



>  arch/x86/kernel/cpu/perf_event_p4.c |    6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> Index: linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c
> =====================================================================
> --- linux-2.6.git.orig/arch/x86/kernel/cpu/perf_event_p4.c
> +++ linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c
> @@ -747,11 +747,11 @@ static int p4_get_escr_idx(unsigned int
>  static int p4_next_cntr(int thread, unsigned long *used_mask,
>                        struct p4_event_bind *bind)
>  {
> -       int i = 0, j;
> +       int i, j;
>
>        for (i = 0; i < P4_CNTR_LIMIT; i++) {
> -               j = bind->cntr[thread][i++];
> -               if (j == -1 || !test_bit(j, used_mask))
> +               j = bind->cntr[thread][i];
> +               if (j != (unsigned char)-1 && !test_bit(j, used_mask))
>                        return j;
>        }
>
>
--
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