1. 31 Mar, 2010 6 commits
    • Steven Rostedt's avatar
      tracing: Show the lost events in the trace_pipe output · bc21b478
      Steven Rostedt authored
      
      
      Now that the ring buffer can keep track of where events are lost.
      Use this information to the output of trace_pipe:
      
             hackbench-3588  [001]  1326.701660: lock_acquire: ffffffff816591e0 read rcu_read_lock
             hackbench-3588  [001]  1326.701661: lock_acquire: ffff88003f4091f0 &(&dentry->d_lock)->rlock
             hackbench-3588  [001]  1326.701664: lock_release: ffff88003f4091f0 &(&dentry->d_lock)->rlock
      CPU:1 [LOST 673 EVENTS]
             hackbench-3588  [001]  1326.702711: kmem_cache_free: call_site=ffffffff81102b85 ptr=ffff880026d96738
             hackbench-3588  [001]  1326.702712: lock_release: ffff88003e1480a8 &mm->mmap_sem
             hackbench-3588  [001]  1326.702713: lock_acquire: ffff88003e1480a8 &mm->mmap_sem
      
      Even works with the function graph tracer:
      
       2) ! 170.098 us  |                                            }
       2)   4.036 us    |                                            rcu_irq_exit();
       2)   3.657 us    |                                            idle_cpu();
       2) ! 190.301 us  |                                          }
      CPU:2 [LOST 2196 EVENTS]
       2)   0.853 us    |                            } /* cancel_dirty_page */
       2)               |                            remove_from_page_cache() {
       2)   1.578 us    |                              _raw_spin_lock_irq();
       2)               |                              __remove_from_page_cache() {
      
      Note, it does not work with the iterator "trace" file, since it requires
      the use of consuming the page from the ring buffer to determine how many
      events were lost, which the iterator does not do.
      Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      bc21b478
    • Steven Rostedt's avatar
      ring-buffer: Add place holder recording of dropped events · 66a8cb95
      Steven Rostedt authored
      
      
      Currently, when the ring buffer drops events, it does not record
      the fact that it did so. It does inform the writer that the event
      was dropped by returning a NULL event, but it does not put in any
      place holder where the event was dropped.
      
      This is not a trivial thing to add because the ring buffer mostly
      runs in overwrite (flight recorder) mode. That is, when the ring
      buffer is full, new data will overwrite old data.
      
      In a produce/consumer mode, where new data is simply dropped when
      the ring buffer is full, it is trivial to add the placeholder
      for dropped events. When there's more room to write new data, then
      a special event can be added to notify the reader about the dropped
      events.
      
      But in overwrite mode, any new write can overwrite events. A place
      holder can not be inserted into the ring buffer since there never
      may be room. A reader could also come in at anytime and miss the
      placeholder.
      
      Luckily, the way the ring buffer works, the read side can find out
      if events were lost or not, and how many events. Everytime a write
      takes place, if it overwrites the header page (the next read) it
      updates a "overrun" variable that keeps track of the number of
      lost events. When a reader swaps out a page from the ring buffer,
      it can record this number, perfom the swap, and then check to
      see if the number changed, and take the diff if it has, which would be
      the number of events dropped. This can be stored by the reader
      and returned to callers of the reader.
      
      Since the reader page swap will fail if the writer moved the head
      page since the time the reader page set up the swap, this gives room
      to record the overruns without worrying about races. If the reader
      sets up the pages, records the overrun, than performs the swap,
      if the swap succeeds, then the overrun variable has not been
      updated since the setup before the swap.
      
      For binary readers of the ring buffer, a flag is set in the header
      of each sub page (sub buffer) of the ring buffer. This flag is embedded
      in the size field of the data on the sub buffer, in the 31st bit (the size
      can be 32 or 64 bits depending on the architecture), but only 27
      bits needs to be used for the actual size (less actually).
      
      We could add a new field in the sub buffer header to also record the
      number of events dropped since the last read, but this will change the
      format of the binary ring buffer a bit too much. Perhaps this change can
      be made if the information on the number of events dropped is considered
      important enough.
      
      Note, the notification of dropped events is only used by consuming reads
      or peeking at the ring buffer. Iterating over the ring buffer does not
      keep this information because the necessary data is only available when
      a page swap is made, and the iterator does not swap out pages.
      
      Cc: Robert Richter <robert.richter@amd.com>
      Cc: Andi Kleen <andi@firstfloor.org>
      Cc: Li Zefan <lizf@cn.fujitsu.com>
      Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
      Cc: "Luis Claudio R. Goncalves" <lclaudio@uudg.org>
      Cc: Frederic Weisbecker <fweisbec@gmail.com>
      Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      66a8cb95
    • Steven Rostedt's avatar
      tracing: Fix compile error in module tracepoints when MODULE_UNLOAD not set · eb0c5377
      Steven Rostedt authored
      
      
      If modules are configured in the build but unloading of modules is not,
      then the refcnt is not defined. Place the get/put module tracepoints
      under CONFIG_MODULE_UNLOAD since it references this field in the module
      structure.
      
      As a side-effect, this patch also reduces the code when MODULE_UNLOAD
      is not set, because these unused tracepoints are not created.
      Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      eb0c5377
    • Li Zefan's avatar
      tracing: Remove side effect from module tracepoints that caused a GPF · ae832d1e
      Li Zefan authored
      
      
      Remove the @refcnt argument, because it has side-effects, and arguments with
      side-effects are not skipped by the jump over disabled instrumentation and are
      executed even when the tracepoint is disabled.
      
      This was also causing a GPF as found by Randy Dunlap:
      
      Subject: 2.6.33 GP fault only when built with tracing
      LKML-Reference: <4BA2B69D.3000309@oracle.com>
      
      Note, the current 2.6.34-rc has a fix for the actual cause of the GPF,
      but this fixes one of its triggers.
      Tested-by: default avatarRandy Dunlap <randy.dunlap@oracle.com>
      Acked-by: default avatarMathieu Desnoyers <mathieu.desnoyers@efficios.com>
      Signed-off-by: default avatarLi Zefan <lizf@cn.fujitsu.com>
      LKML-Reference: <4BA97FA7.6040406@cn.fujitsu.com>
      Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      ae832d1e
    • Li Zefan's avatar
      tracing: Update comments · 50354a8a
      Li Zefan authored
      
      
      Make some comments consistent with the code.
      Signed-off-by: default avatarLi Zefan <lizf@cn.fujitsu.com>
      LKML-Reference: <4BA97FD0.7090202@cn.fujitsu.com>
      Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      50354a8a
    • Li Zefan's avatar
      tracing: Convert some signal events to DEFINE_TRACE · 4bdde044
      Li Zefan authored
      
      
      Use DECLARE_EVENT_CLASS to remove duplicate code:
      
      text    data     bss     dec     hex filename
        23639    6084       8   29731    7423 kernel/signal.o.orig
        22727    6084       8   28819    7093 kernel/signal.o
      
      2 events are converted:
      
        signal_queue_overflow: signal_overflow_fail, signal_lose_info
      
      No functional change.
      Acked-by: default avatarMasami Hiramatsu <mhiramat@redhat.com>
      Signed-off-by: default avatarLi Zefan <lizf@cn.fujitsu.com>
      LKML-Reference: <4BA97FBD.8070703@cn.fujitsu.com>
      Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      4bdde044
  2. 30 Mar, 2010 6 commits
  3. 29 Mar, 2010 28 commits