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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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