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  1. 04 12月, 2014 2 次提交
    • B
      tracing: Add additional marks to signal very large time deltas · 8e1e1df2
      由 Byungchul Park 提交于 
      Currently, function graph tracer prints "!" or "+" just before
function execution time to signal a function overhead, depending
on the time. And some tracers tracing latency also print "!" or
"+" just after time to signal overhead, depending on the interval
between events. Even it is usually enough to do that, we sometimes
need to signal for bigger execution time than 100 micro seconds.

For example, I used function graph tracer to detect if there is
any case that exit_mm() takes too much time. I did following steps
in /sys/kernel/debug/tracing. It was easier to detect very large
excution time with patched kernel than with original kernel.

$ echo exit_mm > set_graph_function
$ echo function_graph > current_tracer
$ echo > trace
$ cat trace_pipe > $LOGFILE
 ... (do something and terminate logging)
$ grep "\\$" $LOGFILE
 3) $ 22082032 us |                      } /* kernel_map_pages */
 3) $ 22082040 us |                    } /* free_pages_prepare */
 3) $ 22082113 us |                  } /* free_hot_cold_page */
 3) $ 22083455 us |                } /* free_hot_cold_page_list */
 3) $ 22083895 us |              } /* release_pages */
 3) $ 22177873 us |            } /* free_pages_and_swap_cache */
 3) $ 22178929 us |          } /* unmap_single_vma */
 3) $ 22198885 us |        } /* unmap_vmas */
 3) $ 22206949 us |      } /* exit_mmap */
 3) $ 22207659 us |    } /* mmput */
 3) $ 22207793 us |  } /* exit_mm */

And then, it was easy to find out that a schedule-out occured by
sub_preempt_count() within kernel_map_pages().

To detect very large function exection time caused by either problematic
function implementation or scheduling issues, this patch can be useful.

Link: http://lkml.kernel.org/r/1416789259-24038-1-git-send-email-byungchul.park@lge.comSigned-off-by: NByungchul Park <byungchul.park@lge.com>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>
      8e1e1df2
    • J
      Documentation: describe trace_buf_size parameter more accurately · 3e6fb8e9
      由 Joonsoo Kim 提交于 
      I'm stuck into panic that too litte free memory is left when I boot with
trace_buf_size parameter. After digging into the problem, I found that
trace_buf_size is the size of trace buffer on each cpu rather than total
size of trace buffer. To prevent victim like me, change description of
trace_buf_size parameter more accurately.

Link: http://lkml.kernel.org/r/1417570760-10620-1-git-send-email-iamjoonsoo.kim@lge.comSigned-off-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>
      3e6fb8e9
  3. 03 12月, 2014 2 次提交
  5. 02 12月, 2014 9 次提交
  7. 25 11月, 2014 1 次提交
    • S
      ftrace/x86: Have static function tracing always test for function graph · 62a207d7
      由 Steven Rostedt (Red Hat) 提交于 
      New updates to the ftrace generic code had ftrace_stub not always being
called when ftrace is off. This causes the static tracer to always save
and restore functions. But it also showed that when function tracing is
running, the function graph tracer can not. We should always check to see
if function graph tracing is running even if the function tracer is running
too. The function tracer code is not the only one that uses the hook to
function mcount.

Cc: Markos Chandras <Markos.Chandras@imgtec.com>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>
      62a207d7
  9. 22 11月, 2014 2 次提交
  11. 21 11月, 2014 1 次提交
  13. 20 11月, 2014 19 次提交
  15. 19 11月, 2014 1 次提交
    • S
      tracing: Fix race of function probes counting · a9ce7c36
      由 Steven Rostedt (Red Hat) 提交于 
      The function probe counting for traceon and traceoff suffered a race
condition where if the probe was executing on two or more CPUs at the
same time, it could decrement the counter by more than one when
disabling (or enabling) the tracer only once.

The way the traceon and traceoff probes are suppose to work is that
they disable (or enable) tracing once per count. If a user were to
echo 'schedule:traceoff:3' into set_ftrace_filter, then when the
schedule function was called, it would disable tracing. But the count
should only be decremented once (to 2). Then if the user enabled tracing
again (via tracing_on file), the next call to schedule would disable
tracing again and the count would be decremented to 1.

But if multiple CPUS called schedule at the same time, it is possible
that the count would be decremented more than once because of the
simple "count--" used.

By reading the count into a local variable and using memory barriers
we can guarantee that the count would only be decremented once per
disable (or enable).

The stack trace probe had a similar race, but here the stack trace will
decrement for each time it is called. But this had the read-modify-
write race, where it could stack trace more than the number of times
that was specified. This case we use a cmpxchg to stack trace only the
number of times specified.

The dump probes can still use the old "update_count()" function as
they only run once, and that is controlled by the dump logic
itself.

Link: http://lkml.kernel.org/r/20141118134643.4b550ee4@gandalf.local.homeSigned-off-by: NSteven Rostedt <rostedt@goodmis.org>
      a9ce7c36
  17. 14 11月, 2014 3 次提交