On Mon, 24 Nov 2014 09:34:19 +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. 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 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 "\\$" $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. > > Signed-off-by: Byungchul Park <[email protected]>
Looks good! 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/
