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]> --- Documentation/trace/ftrace.txt | 10 +++++++--- kernel/trace/trace.h | 2 ++ kernel/trace/trace_functions_graph.c | 7 +------ kernel/trace/trace_output.c | 35 +++++++++++++++++++++++++++++----- 4 files changed, 40 insertions(+), 14 deletions(-) diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt index 4da4261..64efb3e 100644 --- a/Documentation/trace/ftrace.txt +++ b/Documentation/trace/ftrace.txt @@ -680,9 +680,11 @@ The above is mostly meaningful for kernel developers. needs to be fixed to be only relative to the same CPU. The marks are determined by the difference between this current trace and the next trace. - '!' - greater than preempt_mark_thresh (default 100) - '+' - greater than 1 microsecond - ' ' - less than or equal to 1 microsecond. + '$' - greater than 1 second + '#' - greater than 1000 microsecond + '!' - greater than 100 microsecond + '+' - greater than 10 microsecond + ' ' - less than or equal to 10 microsecond. The rest is the same as the 'trace' file. @@ -1951,6 +1953,8 @@ want, depending on your needs. + means that the function exceeded 10 usecs. ! means that the function exceeded 100 usecs. + # means that the function exceeded 1000 usecs. + $ means that the function exceeded 1 sec. - The task/pid field displays the thread cmdline and pid which diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index 385391f..0aaf10d 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -719,6 +719,8 @@ enum print_line_t print_trace_line(struct trace_iterator *iter); extern unsigned long trace_flags; +extern char trace_find_mark(unsigned long long duration); + /* Standard output formatting function used for function return traces */ #ifdef CONFIG_FUNCTION_GRAPH_TRACER diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c index cb33f46..1ecb1ad 100644 --- a/kernel/trace/trace_functions_graph.c +++ b/kernel/trace/trace_functions_graph.c @@ -822,12 +822,7 @@ 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 100 usecs */ - if (duration > 100000ULL) - ret = trace_seq_puts(s, "! "); - /* Duration exceeded 10 usecs */ - else if (duration > 10000ULL) - ret = trace_seq_puts(s, "+ "); + ret = trace_seq_printf(s, "%c ", trace_find_mark(duration)); } /* diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c index c6977d5..8d19f3d 100644 --- a/kernel/trace/trace_output.c +++ b/kernel/trace/trace_output.c @@ -124,7 +124,7 @@ ftrace_print_symbols_seq(struct trace_seq *p, unsigned long val, if (ret == (const char *)(trace_seq_buffer_ptr(p))) trace_seq_printf(p, "0x%lx", val); - + trace_seq_putc(p, 0); return ret; @@ -471,7 +471,33 @@ lat_print_generic(struct trace_seq *s, struct trace_entry *entry, int cpu) return trace_print_lat_fmt(s, entry); } -static unsigned long preempt_mark_thresh_us = 100; +#undef MARK +#define MARK(v, s) {.val = v, .sym = s} +/* trace overhead mark */ +static const struct trace_mark { + unsigned long long val; /* unit: nsec */ + char sym; +} mark[] = { + MARK(1000000000ULL , '$'), /* 1 sec */ + MARK(1000000ULL , '#'), /* 1000 usecs */ + MARK(100000ULL , '!'), /* 100 usecs */ + MARK(10000ULL , '+'), /* 10 usecs */ + MARK(0ULL , ' '), /* 0 usecs */ +}; +#undef MARK + +char trace_find_mark(unsigned long long d) +{ + int i; + int size = ARRAY_SIZE(mark); + + for (i = 0; i < size; i++) { + if (d >= mark[i].val) + break; + } + + return (i == size)? ' ' : mark[i].sym; +} static int lat_print_timestamp(struct trace_iterator *iter, u64 next_ts) @@ -506,8 +532,7 @@ lat_print_timestamp(struct trace_iterator *iter, u64 next_ts) return trace_seq_printf( s, " %4lldus%c: ", abs_ts, - rel_ts > preempt_mark_thresh_us ? '!' : - rel_ts > 1 ? '+' : ' '); + trace_find_mark(rel_ts * NSEC_PER_USEC)); } else { /* !verbose && !in_ns */ return trace_seq_printf(s, " %4lld: ", abs_ts); } @@ -692,7 +717,7 @@ int register_ftrace_event(struct trace_event *event) goto out; } else { - + event->type = next_event_type++; list = &ftrace_event_list; } -- 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/
