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    SubjectRe: [PATCH 5/6] perf_counter: add more context information

    * Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:

    > Put in counts to tell which ips belong to what context.
    >
    > -----
    > | | hv
    > | --
    > nr | | kernel
    > | --
    > | | user
    > -----

    btw., i have an observation about the format:

    > -#define MAX_STACK_DEPTH 255
    > +#define MAX_STACK_DEPTH 254
    >
    > struct perf_callchain_entry {
    > - u64 nr;
    > + u32 nr, hv, kernel, user;
    > u64 ip[MAX_STACK_DEPTH];
    > };

    For the special case of signal notifications, if the signal is
    delivered immediately to the same task that raised it (pid=0), the
    call chain is actually a still meaningful one: it is the stack that
    is below the currently executing signal handler context.

    Wouldnt it make sense to record the full stack frame for that case,
    to allow walking/unwinding of the stack? Or can user-space do that
    just fine, based on its own signal context?

    We are going to hard-code the "call-chain is a series of IPs,
    nothing else" model, and i'd like to make sure it's future-proof :)

    Ingo


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