The existing sort keys are less useful for tracepoint events in that
they are always sampled at the same place, the function where the
tracepoint is located.

For example, a 'perf report' on sched:sched_switch event looks like the
following:

  # Overhead  Command          Shared Object     Symbol
  # ........  ...............  ................  ..............
  #
      47.22%  swapper          [kernel.vmlinux]  [k] __schedule
      21.67%  transmission-gt  [kernel.vmlinux]  [k] __schedule
       8.23%  netctl-auto      [kernel.vmlinux]  [k] __schedule
       5.53%  kworker/0:1H     [kernel.vmlinux]  [k] __schedule
       1.98%  Xephyr           [kernel.vmlinux]  [k] __schedule
       1.33%  irq/33-iwlwifi   [kernel.vmlinux]  [k] __schedule
       1.17%  wpa_cli          [kernel.vmlinux]  [k] __schedule
       1.13%  rcu_preempt      [kernel.vmlinux]  [k] __schedule
       0.85%  ksoftirqd/0      [kernel.vmlinux]  [k] __schedule
       0.77%  Timer            [kernel.vmlinux]  [k] __schedule

In fact, tracepoints have meaningful information in their fields but
there's no way to use in 'perf report' currently.  The dynamic sort keys
are introduced in this patc to overcome this limitation.

The sched:sched_switch events have following fields:

  # sudo cat /sys/kernel/debug/tracing/events/sched/sched_switch/format
  name: sched_switch
  ID: 268
  format:
	field:unsigned short common_type;         offset:0; size:2; signed:0;
	field:unsigned char common_flags;         offset:2; size:1; signed:0;
	field:unsigned char common_preempt_count; offset:3; size:1; signed:0;
	field:int common_pid;                     offset:4; size:4; signed:1;

	field:char prev_comm[16]; offset:8;  size:16; signed:1;
	field:pid_t prev_pid;     offset:24; size:4;  signed:1;
	field:int prev_prio;      offset:28; size:4;  signed:1;
	field:long prev_state;    offset:32; size:8;  signed:1;
	field:char next_comm[16]; offset:40; size:16; signed:1;
	field:pid_t next_pid;     offset:56; size:4;  signed:1;
	field:int next_prio;      offset:60; size:4;  signed:1;

  print fmt: "prev_comm=%s prev_pid=%d prev_prio=%d prev_state=%s%s ==>
              next_comm=%s next_pid=%d next_prio=%d",
    REC->prev_comm, REC->prev_pid, REC->prev_prio,
    REC->prev_state & (2048-1) ? __print_flags(REC->prev_state & (2048-1),
    "|", { 1, "S"} , { 2, "D" }, { 4, "T" }, { 8, "t" }, { 16, "Z" }, { 32, "X" },
    { 64, "x" }, { 128, "K"}, { 256, "W" }, { 512, "P" }, { 1024, "N" }) : "R",
    REC->prev_state & 2048 ? "+" : "", REC->next_comm, REC->next_pid, REC->next_prio

With dynamic sort keys, you can use <event.field> as a sort key.  Those
dynamic keys are checked and created on demand.  For instance, below is
to sort by next_pid field output on the same data file:

  $ perf report -s comm,sched:sched_switch.next_pid --stdio
  ...
  # Overhead  Command            next_pid
  # ........  ...............  ..........
  #
      21.23%  transmission-gt           0
      20.86%  swapper               17773
       6.62%  netctl-auto               0
       5.25%  swapper                 109
       5.21%  kworker/0:1H              0
       1.98%  Xephyr                    0
       1.98%  swapper                6524
       1.98%  swapper               27478
       1.37%  swapper               27476
       1.17%  swapper                 233

Multiple dynamic sort keys are also supported:

  $ perf report -s comm,sched:sched_switch.next_pid,sched:sched_switch.next_comm --stdio
  ...
  # Overhead  Command            next_pid         next_comm
  # ........  ...............  ..........  ................
  #
      20.86%  swapper               17773   transmission-gt
       9.64%  transmission-gt           0         swapper/0
       9.16%  transmission-gt           0         swapper/2
       5.25%  swapper                 109      kworker/0:1H
       5.21%  kworker/0:1H              0         swapper/0
       2.14%  netctl-auto               0         swapper/2
       1.98%  netctl-auto               0         swapper/0
       1.98%  swapper                6524            Xephyr
       1.98%  swapper               27478       netctl-auto
       1.78%  transmission-gt           0         swapper/3
       1.53%  Xephyr                    0         swapper/0
       1.29%  netctl-auto               0         swapper/1
       1.29%  swapper               27476       netctl-auto
       1.21%  netctl-auto               0         swapper/3
       1.17%  swapper                 233    irq/33-iwlwifi

Note that pid 0 exists for each cpu so have comm of 'swapper/N'.
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1450804030-29193-6-git-send-email-namhyung@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>