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Subject: Re: Perf events warning..
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
        linux-kernel@vger.kernel.org
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Date: Tue, 15 May 2012 00:20:48 +0200
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On Fri, 2012-05-11 at 08:43 -0700, Linus Torvalds wrote:
> Peter, Ingo, Arnaldo,
>  google doesn't find a warning like this, so it can't be *too*
> commonly reported.
> 
> Anyway, doing some profiling of git "make test" (wonderful load for
> doing lots of small processes that do lots of page faults etc), this
> WARN_ON_ONCE() triggered:
> 
>     ------------[ cut here ]------------
>     WARNING: at kernel/events/core.c:2066 task_ctx_sched_out+0x63/0x70()
>     Hardware name: System Product Name
>     Pid: 18120, comm: git Not tainted 3.4.0-rc6-00089-g4a01c681d58f-dirty #3
>     Call Trace:
>      [<ffffffff810308c5>] warn_slowpath_common+0x75/0xb0
>      [<ffffffff810309c5>] warn_slowpath_null+0x15/0x20
>      [<ffffffff81096d63>] task_ctx_sched_out+0x63/0x70
>      [<ffffffff8109af06>] perf_event_comm+0x1d6/0x2e0
>      [<ffffffff81368ba8>] ? get_random_int+0x88/0xb0
>      [<ffffffff8102e1e2>] ? __mmdrop+0x62/0x90
>      [<ffffffff810e1f93>] set_task_comm+0x63/0x80
>      [<ffffffff810e3206>] setup_new_exec+0x86/0x250
>      [<ffffffff81126b69>] load_elf_binary+0x389/0x1930
>      [<ffffffff81125222>] ? load_misc_binary+0x292/0x390
>      [<ffffffff810bcbdd>] ? get_user_pages+0x4d/0x50
>      [<ffffffff810e13b2>] ? get_arg_page+0xa2/0xd0
>      [<ffffffff810e2b65>] search_binary_handler+0xd5/0x200
>      [<ffffffff811267e0>] ? elf_map+0x170/0x170
>      [<ffffffff810e300d>] do_execve_common.clone.39+0x37d/0x430
>      [<ffffffff810e30d6>] do_execve+0x16/0x20
>      [<ffffffff8100ab75>] sys_execve+0x45/0x70
>      [<ffffffff816b10ac>] stub_execve+0x6c/0xc0
>     ---[ end trace 6fccf3db70f1b560 ]---
> 
> any comments/ideas?

So far I can't make any of the things I came up stick. You ran something
simple like: 'perf record -e cycles:pp -F 20000 make test' ? Or did you
do something more interesting?

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