From: Li Zefan We found that even enabling a single trace event that will rarely be triggered can add big overhead to context switch. (lmbench context switch test) ------------------------------------------------- 2p/0K 2p/16K 2p/64K 8p/16K 8p/64K 16p/16K 16p/64K ctxsw ctxsw ctxsw ctxsw ctxsw ctxsw ctxsw ------ ------ ------ ------ ------ ------- ------- 2.19 2.3 2.21 2.56 2.13 2.54 2.07 2.39 2.51 2.35 2.75 2.27 2.81 2.24 The overhead is 6% ~ 11%. It's because when a trace event is enabled 3 tracepoints (sched_switch, sched_wakeup, sched_wakeup_new) will be activated to map pid to cmdname. We'd like to avoid this overhead, so add a trace option '(no)record-cmd' to allow to disable cmdline recording. Signed-off-by: Li Zefan LKML-Reference: <4C2D57F4.2050204@cn.fujitsu.com> Signed-off-by: Steven Rostedt --- include/linux/ftrace_event.h | 7 +++++-- kernel/trace/trace.c | 6 +++++- kernel/trace/trace.h | 3 +++ kernel/trace/trace_events.c | 30 ++++++++++++++++++++++++++++-- 4 files changed, 41 insertions(+), 5 deletions(-) diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h index 01df7ca..2b7b139 100644 --- a/include/linux/ftrace_event.h +++ b/include/linux/ftrace_event.h @@ -152,11 +152,13 @@ extern int ftrace_event_reg(struct ftrace_event_call *event, enum { TRACE_EVENT_FL_ENABLED_BIT, TRACE_EVENT_FL_FILTERED_BIT, + TRACE_EVENT_FL_RECORDED_CMD_BIT, }; enum { - TRACE_EVENT_FL_ENABLED = (1 << TRACE_EVENT_FL_ENABLED_BIT), - TRACE_EVENT_FL_FILTERED = (1 << TRACE_EVENT_FL_FILTERED_BIT), + TRACE_EVENT_FL_ENABLED = (1 << TRACE_EVENT_FL_ENABLED_BIT), + TRACE_EVENT_FL_FILTERED = (1 << TRACE_EVENT_FL_FILTERED_BIT), + TRACE_EVENT_FL_RECORDED_CMD = (1 << TRACE_EVENT_FL_RECORDED_CMD_BIT), }; struct ftrace_event_call { @@ -174,6 +176,7 @@ struct ftrace_event_call { * 32 bit flags: * bit 1: enabled * bit 2: filter_active + * bit 3: enabled cmd record * * Changes to flags must hold the event_mutex. * diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 8683dec..af90429 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -344,7 +344,7 @@ static DECLARE_WAIT_QUEUE_HEAD(trace_wait); /* trace_flags holds trace_options default values */ unsigned long trace_flags = TRACE_ITER_PRINT_PARENT | TRACE_ITER_PRINTK | TRACE_ITER_ANNOTATE | TRACE_ITER_CONTEXT_INFO | TRACE_ITER_SLEEP_TIME | - TRACE_ITER_GRAPH_TIME; + TRACE_ITER_GRAPH_TIME | TRACE_ITER_RECORD_CMD; static int trace_stop_count; static DEFINE_SPINLOCK(tracing_start_lock); @@ -428,6 +428,7 @@ static const char *trace_options[] = { "latency-format", "sleep-time", "graph-time", + "record-cmd", NULL }; @@ -2561,6 +2562,9 @@ static void set_tracer_flags(unsigned int mask, int enabled) trace_flags |= mask; else trace_flags &= ~mask; + + if (mask == TRACE_ITER_RECORD_CMD) + trace_event_enable_cmd_record(enabled); } static ssize_t diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index 84d3f12..7778f06 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -591,6 +591,7 @@ enum trace_iterator_flags { TRACE_ITER_LATENCY_FMT = 0x20000, TRACE_ITER_SLEEP_TIME = 0x40000, TRACE_ITER_GRAPH_TIME = 0x80000, + TRACE_ITER_RECORD_CMD = 0x100000, }; /* @@ -723,6 +724,8 @@ filter_check_discard(struct ftrace_event_call *call, void *rec, return 0; } +extern void trace_event_enable_cmd_record(bool enable); + extern struct mutex event_mutex; extern struct list_head ftrace_events; diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index e8e6043..09b4fa6 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -170,6 +170,26 @@ int ftrace_event_reg(struct ftrace_event_call *call, enum trace_reg type) } EXPORT_SYMBOL_GPL(ftrace_event_reg); +void trace_event_enable_cmd_record(bool enable) +{ + struct ftrace_event_call *call; + + mutex_lock(&event_mutex); + list_for_each_entry(call, &ftrace_events, list) { + if (!(call->flags & TRACE_EVENT_FL_ENABLED)) + continue; + + if (enable) { + tracing_start_cmdline_record(); + call->flags |= TRACE_EVENT_FL_RECORDED_CMD; + } else { + tracing_stop_cmdline_record(); + call->flags &= ~TRACE_EVENT_FL_RECORDED_CMD; + } + } + mutex_unlock(&event_mutex); +} + static int ftrace_event_enable_disable(struct ftrace_event_call *call, int enable) { @@ -179,13 +199,19 @@ static int ftrace_event_enable_disable(struct ftrace_event_call *call, case 0: if (call->flags & TRACE_EVENT_FL_ENABLED) { call->flags &= ~TRACE_EVENT_FL_ENABLED; - tracing_stop_cmdline_record(); + if (call->flags & TRACE_EVENT_FL_RECORDED_CMD) { + tracing_stop_cmdline_record(); + call->flags &= ~TRACE_EVENT_FL_RECORDED_CMD; + } call->class->reg(call, TRACE_REG_UNREGISTER); } break; case 1: if (!(call->flags & TRACE_EVENT_FL_ENABLED)) { - tracing_start_cmdline_record(); + if (trace_flags & TRACE_ITER_RECORD_CMD) { + tracing_start_cmdline_record(); + call->flags |= TRACE_EVENT_FL_RECORDED_CMD; + } ret = call->class->reg(call, TRACE_REG_REGISTER); if (ret) { tracing_stop_cmdline_record(); -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/