• S
    tracing: profile likely and unlikely annotations · 1f0d69a9
    Steven Rostedt 提交于
    Impact: new unlikely/likely profiler
    
    Andrew Morton recently suggested having an in-kernel way to profile
    likely and unlikely macros. This patch achieves that goal.
    
    When configured, every(*) likely and unlikely macro gets a counter attached
    to it. When the condition is hit, the hit and misses of that condition
    are recorded. These numbers can later be retrieved by:
    
      /debugfs/tracing/profile_likely    - All likely markers
      /debugfs/tracing/profile_unlikely  - All unlikely markers.
    
    # cat /debug/tracing/profile_unlikely | head
     correct incorrect  %        Function                  File              Line
     ------- ---------  -        --------                  ----              ----
        2167        0   0 do_arch_prctl                  process_64.c         832
           0        0   0 do_arch_prctl                  process_64.c         804
        2670        0   0 IS_ERR                         err.h                34
       71230     5693   7 __switch_to                    process_64.c         673
       76919        0   0 __switch_to                    process_64.c         639
       43184    33743  43 __switch_to                    process_64.c         624
       12740    64181  83 __switch_to                    process_64.c         594
       12740    64174  83 __switch_to                    process_64.c         590
    
    # cat /debug/tracing/profile_unlikely | \
      awk '{ if ($3 > 25) print $0; }' |head -20
       44963    35259  43 __switch_to                    process_64.c         624
       12762    67454  84 __switch_to                    process_64.c         594
       12762    67447  84 __switch_to                    process_64.c         590
        1478      595  28 syscall_get_error              syscall.h            51
           0     2821 100 syscall_trace_leave            ptrace.c             1567
           0        1 100 native_smp_prepare_cpus        smpboot.c            1237
       86338   265881  75 calc_delta_fair                sched_fair.c         408
      210410   108540  34 calc_delta_mine                sched.c              1267
           0    54550 100 sched_info_queued              sched_stats.h        222
       51899    66435  56 pick_next_task_fair            sched_fair.c         1422
           6       10  62 yield_task_fair                sched_fair.c         982
        7325     2692  26 rt_policy                      sched.c              144
           0     1270 100 pre_schedule_rt                sched_rt.c           1261
        1268    48073  97 pick_next_task_rt              sched_rt.c           884
           0    45181 100 sched_info_dequeued            sched_stats.h        177
           0       15 100 sched_move_task                sched.c              8700
           0       15 100 sched_move_task                sched.c              8690
       53167    33217  38 schedule                       sched.c              4457
           0    80208 100 sched_info_switch              sched_stats.h        270
       30585    49631  61 context_switch                 sched.c              2619
    
    # cat /debug/tracing/profile_likely | awk '{ if ($3 > 25) print $0; }'
       39900    36577  47 pick_next_task                 sched.c              4397
       20824    15233  42 switch_mm                      mmu_context_64.h     18
           0        7 100 __cancel_work_timer            workqueue.c          560
         617    66484  99 clocksource_adjust             timekeeping.c        456
           0   346340 100 audit_syscall_exit             auditsc.c            1570
          38   347350  99 audit_get_context              auditsc.c            732
           0   345244 100 audit_syscall_entry            auditsc.c            1541
          38     1017  96 audit_free                     auditsc.c            1446
           0     1090 100 audit_alloc                    auditsc.c            862
        2618     1090  29 audit_alloc                    auditsc.c            858
           0        6 100 move_masked_irq                migration.c          9
           1      198  99 probe_sched_wakeup             trace_sched_switch.c 58
           2        2  50 probe_wakeup                   trace_sched_wakeup.c 227
           0        2 100 probe_wakeup_sched_switch      trace_sched_wakeup.c 144
        4514     2090  31 __grab_cache_page              filemap.c            2149
       12882   228786  94 mapping_unevictable            pagemap.h            50
           4       11  73 __flush_cpu_slab               slub.c               1466
      627757   330451  34 slab_free                      slub.c               1731
        2959    61245  95 dentry_lru_del_init            dcache.c             153
         946     1217  56 load_elf_binary                binfmt_elf.c         904
         102       82  44 disk_put_part                  genhd.h              206
           1        1  50 dst_gc_task                    dst.c                82
           0       19 100 tcp_mss_split_point            tcp_output.c         1126
    
    As you can see by the above, there's a bit of work to do in rethinking
    the use of some unlikelys and likelys. Note: the unlikely case had 71 hits
    that were more than 25%.
    
    Note:  After submitting my first version of this patch, Andrew Morton
      showed me a version written by Daniel Walker, where I picked up
      the following ideas from:
    
      1)  Using __builtin_constant_p to avoid profiling fixed values.
      2)  Using __FILE__ instead of instruction pointers.
      3)  Using the preprocessor to stop all profiling of likely
           annotations from vsyscall_64.c.
    
    Thanks to Andrew Morton, Arjan van de Ven, Theodore Tso and Ingo Molnar
    for their feed back on this patch.
    
    (*) Not ever unlikely is recorded, those that are used by vsyscalls
     (a few of them) had to have profiling disabled.
    Signed-off-by: NSteven Rostedt <srostedt@redhat.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Frederic Weisbecker <fweisbec@gmail.com>
    Cc: Theodore Tso <tytso@mit.edu>
    Cc: Arjan van de Ven <arjan@infradead.org>
    Cc: Steven Rostedt <srostedt@redhat.com>
    Signed-off-by: NIngo Molnar <mingo@elte.hu>
    1f0d69a9
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