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SubjectRe: [PATCH v2 00/16] perf: add memory access sampling support
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Hi Arnaldo,

On Tue, 6 Nov 2012 17:52:21 -0300, Arnaldo Carvalho de Melo wrote:
> Em Mon, Nov 05, 2012 at 02:50:47PM +0100, Stephane Eranian escreveu:
> [root@sandy acme]# perf mem -t load rep --stdio --sort=symbol,symbol_daddr,cost
> # Samples: 30 of event 'cpu/mem-loads/pp'
> # Total cost : 640
> # Sort order : symbol,symbol_daddr,cost
> #
> # Overhead Samples Symbol Data Symbol Cost
> # ........ ........... ...................... ...................... .......
> #
> 55.00% 1 [k] lookup_fast [k] 0xffff8803b7521bd4 352
> 5.47% 1 [k] cache_alloc_refill [k] 0xffff880407705024 35
> 3.44% 1 [k] cache_alloc_refill [k] 0xffff88041d8527d8 22
> 3.28% 1 [k] run_timer_softirq [k] 0xffff88041e2c3e90 21
> 2.50% 1 [k] __list_add [k] 0xffff8803b7521d68 16
> 2.19% 1 [.] __strcoll_l [.] 0x00007fffa8d44080 14
> 1.88% 1 [.] __strcoll_l [.] 0x00007fffa8d44104 12
>
> If we go to the annotation browser to see where is that lookup_fast hitting we get:
>
> 100.00 │ mov -0x34(%rbp),%eax
>
> How to map 0xffff8803b7521bd4 to a stack variable, struct members and all?
>
> Humm, for userspace we have PERF_SAMPLE_REGS_USER for the dwarf unwinder we
> need for userspace, but what about reverse mapping of kernel variables? Jiri?

I suspect there aren't much thing we can do on stack. One thing we can
do is adding dso_daddr to sort key and seeing it's a [stack] (or
[stack:tid]) or not. But not sure it can be done for kernel stacks too.

Thanks,
Namhyung
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