On Thu, 23 Oct 2014 17:17:22 +0900 [email protected] wrote: > From: Byungchul Park <[email protected]> > > Currently, function graph tracer prints "!" or "+" just before > function execution time to signal a function overhead, depending > on the time. Even it is usually enough to do that, we sometimes > need to be signaled 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 big > 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 "!s" $LOGFILE > 3) !s22082032 us | } /* kernel_map_pages */ > 3) !s22082040 us | } /* free_pages_prepare */ > 3) !s22082113 us | } /* free_hot_cold_page */ > 3) !s22083455 us | } /* free_hot_cold_page_list */ > 3) !s22083895 us | } /* release_pages */ > 3) !s22177873 us | } /* free_pages_and_swap_cache */ > 3) !s22178929 us | } /* unmap_single_vma */ > 3) !s22198885 us | } /* unmap_vmas */ > 3) !s22206949 us | } /* exit_mmap */ > 3) !s22207659 us | } /* mmput */ > 3) !s22207793 us | } /* exit_mm */
Hmm, I wonder if a "s!" is better. Having the 's' next to the number seems to make it look like some strange number. Maybe we should still keep this cryptic. We can update the debugfs/tracing/README to add the meanings as well. But perhaps have: + == > 10usec ! == > 100usec * == > 1msec $ == > 1sec > > 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 either by problematic > function implementation or by scheduling issues, this patch can be > useful. > > Signed-off-by: Byungchul Park <[email protected]> > --- > kernel/trace/trace_functions_graph.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/kernel/trace/trace_functions_graph.c > b/kernel/trace/trace_functions_graph.c > index c18a1e3..ea8b7e7 100644 > --- a/kernel/trace/trace_functions_graph.c > +++ b/kernel/trace/trace_functions_graph.c > @@ -822,8 +822,14 @@ print_graph_duration(unsigned long long duration, struct > trace_seq *s, > > /* Signal a overhead of time execution to the output */ > if (flags & TRACE_GRAPH_PRINT_OVERHEAD) { > + /* Duration exceeded 1 secs */ > + if (duration > 1000000000ULL) > + ret = trace_seq_puts(s, "!s"); > + /* Duration exceeded 1 msecs */ > + else if (duration > 1000000ULL) > + ret = trace_seq_puts(s, "!m"); > /* Duration exceeded 100 usecs */ > - if (duration > 100000ULL) > + else if (duration > 100000ULL) > ret = trace_seq_puts(s, "! "); > /* Duration exceeded 10 usecs */ > else if (duration > 10000ULL) also, the documentation in Documentation/trace/ftrace.txt must be updated with this patch. Make sure you update the function graph part and not the "time:" and "delay:" section. Come to think of it. Could you make another patch that adds this to the normal delay as well? And we should make the "normal" '+' mean 10usecs instead of 1usec. 1 is rather meaningless and inconsistent with the graph tracer. Thanks! -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
