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    SubjectRe: [PATCH v2 00/16] perf: add memory access sampling support
    Em Mon, Nov 05, 2012 at 02:50:47PM +0100, Stephane Eranian escreveu:
    > Or if one is interested in the data view:
    > $ perf mem -t load rep --sort=symbol_daddr,cost
    > # Samples: 19K of event 'cpu/mem-loads/pp'
    > # Total cost : 1013994
    > # Sort order : symbol_daddr,cost
    > #
    > # Overhead Samples Data Symbol Cost
    > # ........ ........... ...................... .......
    > #
    > 0.10% 1 [.] 0x00007f67dffe8038 986
    > 0.09% 1 [.] 0x00007f67df91a750 890
    > 0.08% 1 [.] 0x00007f67e288fba8 826
    >

    > CAVEAT: Note that the data addresses are not resolved correctly currently due to a
    > problem in perf data symbol resolution code which I have not been able to
    > uncover so far.

    Stephane,

    Those data addresses mostly are on the stack, we need reverse
    resolution using DWARF location expressions to figure out what is the
    name of a variable that is on a particular address, etc.

    Masami, have you played with this already? I mean:

    [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?

    - Arnaldo
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