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 */ 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) -- 1.7.9.5 -- 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/
