linux-kernel - Re: [PATCH] perf tool: Ensure forward progress unwinding frames

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Date:	Sun, 08 Dec 2013 10:46:13 -0700
From:	David Ahern <dsahern@...il.com>
To:	acme@...stprotocols.net, linux-kernel@...r.kernel.org,
	Jiri Olsa <jolsa@...hat.com>
CC:	David Ahern <dsahern@...il.com>
Subject: Re: [PATCH] perf tool: Ensure forward progress unwinding frames

ping.. Jiri, any thoughts on this?

On 12/1/13, 5:01 PM, David Ahern wrote:
> The dwarf option for callstacks is getting stuck on the unwind and showing
> repeated frames. For example,
>
> qemu-system-x86 13759 [001] 287663.084957: syscalls:sys_enter_futex: uaddr: 0x7f770a958700, op: 0x00000081, val: 0x00000001, utime: 0x7f75ea
>              7f7705fd23ea __lll_unlock_wake (/lib64/libpthread-2.14.90.so)
>              7f7705fcf045 _L_unlock_649 (/lib64/libpthread-2.14.90.so)
>              7f7705fcf045 _L_unlock_649 (/lib64/libpthread-2.14.90.so)
>              7f7705fcf045 _L_unlock_649 (/lib64/libpthread-2.14.90.so)
>              7f7705fcf045 _L_unlock_649 (/lib64/libpthread-2.14.90.so)
>              7f7705fcf045 _L_unlock_649 (/lib64/libpthread-2.14.90.so)
>              ...
>              (Last frame repeats 126 times)
>
> Catch that the same frame is hit multiple times and break out of the loop.
>
> With this patch:
>
> qemu-system-x86 13759 [001] 287663.084967: syscalls:sys_exit_futex: 0x1
>              7f7705fd23ea __lll_unlock_wake (/lib64/libpthread-2.14.90.so)
>              7f7705fcf045 _L_unlock_649 (/lib64/libpthread-2.14.90.so)
>
> Signed-off-by: David Ahern <dsahern@...il.com>
> Cc: Jiri Olsa <jolsa@...hat.com>
> ---
>   tools/perf/util/unwind.c | 5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/tools/perf/util/unwind.c b/tools/perf/util/unwind.c
> index 0efd5393de85..817ffc1f3a00 100644
> --- a/tools/perf/util/unwind.c
> +++ b/tools/perf/util/unwind.c
> @@ -563,6 +563,7 @@ static int get_entries(struct unwind_info *ui, unwind_entry_cb_t cb,
>   {
>   	unw_addr_space_t addr_space;
>   	unw_cursor_t c;
> +	unw_word_t prev_ip = 0;
>   	int ret;
>
>   	addr_space = unw_create_addr_space(&accessors, 0);
> @@ -579,6 +580,10 @@ static int get_entries(struct unwind_info *ui, unwind_entry_cb_t cb,
>   		unw_word_t ip;
>
>   		unw_get_reg(&c, UNW_REG_IP, &ip);
> +		if (ip == prev_ip)
> +			break;
> +		prev_ip = ip;
> +
>   		ret = entry(ip, ui->thread, ui->machine, cb, arg);
>   	}
>
>

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