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SubjectRe: [PATCH] powerpc/perf_events: Implement perf_arch_fetch_caller_regs for powerpc
On Mon, Mar 15, 2010 at 10:04:54PM +0100, Frederic Weisbecker wrote:
> On Mon, Mar 15, 2010 at 04:46:15PM +1100, Paul Mackerras wrote:

> > 14.99% perf [kernel.kallsyms] [k] ._raw_spin_lock
> > |
> > --- ._raw_spin_lock
> > |
> > |--25.00%-- .alloc_fd
> > | (nil)
> > | |
> > | |--50.00%-- .anon_inode_getfd
> > | | .sys_perf_event_open
> > | | syscall_exit
> > | | syscall
> > | | create_counter
> > | | __cmd_record
> > | | run_builtin
> > | | main
> > | | 0xfd2e704
> > | | 0xfd2e8c0
> > | | (nil)
> >
> > ... etc.
> >
> > Signed-off-by: Paul Mackerras <paulus@samba.org>
>
>
> Cool!

By the way, I notice that gcc tends to inline the tracing functions,
which means that by going up 2 stack frames we miss some of the
functions. For example, for the lock:lock_acquire event, we have
_raw_spin_lock() -> lock_acquire() -> trace_lock_acquire() ->
perf_trace_lock_acquire() -> perf_trace_templ_lock_acquire() ->
perf_fetch_caller_regs() -> perf_arch_fetch_caller_regs().

But in the ppc64 kernel binary I just built, gcc inlined
trace_lock_acquire in lock_acquire, and perf_trace_templ_lock_acquire
in perf_trace_lock_acquire. Given that perf_fetch_caller_regs is
explicitly inlined, going up two levels from perf_fetch_caller_regs
gets us to _raw_spin_lock, whereas I think you intended it to get us
to trace_lock_acquire. I'm not sure what to do about that - any
thoughts?

Paul.


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