LBR only collect the user call stack. To reconstruct a call stack, both
kernel call stack and user call stack are required. The function
resolve_lbr_callchain_sample() mix the kernel call stack and user call
stack.

Now, with the help of HW idx, perf tool can reconstruct a more complete
call stack by adding some user call stack from previous sample. However,
current implementation is hard to be extended to support it.

Current code path for resolve_lbr_callchain_sample()

  for (j = 0; j < mix_chain_nr; j++) {
       if (ORDER_CALLEE) {
             if (kernel callchain)
                  Fill callchain info
             else if (LBR callchain)
                  Fill callchain info
       } else {
             if (LBR callchain)
                  Fill callchain info
             else if (kernel callchain)
                  Fill callchain info
       }
       add_callchain_ip();
  }

With the patch,

  if (ORDER_CALLEE) {
       for (j = 0; j < NUM of kernel callchain) {
             Fill callchain info
             add_callchain_ip();
       }
       for (; j < mix_chain_nr) {
             Fill callchain info
             add_callchain_ip();
       }
  } else {
       for (; j < NUM of LBR callchain) {
             Fill callchain info
             add_callchain_ip();
       }
       for (j = 0; j < mix_chain_nr) {
             Fill callchain info
             add_callchain_ip();
       }
  }

No functional changes.
Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexey Budankov <alexey.budankov@linux.intel.com>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Pavel Gerasimov <pavel.gerasimov@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Vitaly Slobodskoy <vitaly.slobodskoy@intel.com>
Link: http://lore.kernel.org/lkml/20200319202517.23423-7-kan.liang@linux.intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>