From e870e9a1240bcef1157ffaaf71dac63362e71904 Mon Sep 17 00:00:00 2001 From: Li Zefan Date: Fri, 2 Jul 2010 11:07:32 +0800 Subject: tracing: Allow to disable cmdline recording 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 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) (limited to 'include/linux/ftrace_event.h') diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h index 01df7ca4ead7..2b7b1395b4d5 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. * -- cgit v1.2.2 From bc289ae98b75d93228d24f521ef02a076e506e94 Mon Sep 17 00:00:00 2001 From: Lai Jiangshan Date: Thu, 3 Jun 2010 18:26:24 +0800 Subject: tracing: Reduce latency and remove percpu trace_seq __print_flags() and __print_symbolic() use percpu trace_seq: 1) Its memory is allocated at compile time, it wastes memory if we don't use tracing. 2) It is percpu data and it wastes more memory for multi-cpus system. 3) It disables preemption when it executes its core routine "trace_seq_printf(s, "%s: ", #call);" and introduces latency. So we move this trace_seq to struct trace_iterator. Signed-off-by: Lai Jiangshan LKML-Reference: <4C078350.7090106@cn.fujitsu.com> Signed-off-by: Steven Rostedt --- include/linux/ftrace_event.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'include/linux/ftrace_event.h') diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h index 2b7b1395b4d5..02b8b24f8f51 100644 --- a/include/linux/ftrace_event.h +++ b/include/linux/ftrace_event.h @@ -11,8 +11,6 @@ struct trace_array; struct tracer; struct dentry; -DECLARE_PER_CPU(struct trace_seq, ftrace_event_seq); - struct trace_print_flags { unsigned long mask; const char *name; @@ -58,6 +56,9 @@ struct trace_iterator { struct ring_buffer_iter *buffer_iter[NR_CPUS]; unsigned long iter_flags; + /* trace_seq for __print_flags() and __print_symbolic() etc. */ + struct trace_seq tmp_seq; + /* The below is zeroed out in pipe_read */ struct trace_seq seq; struct trace_entry *ent; -- cgit v1.2.2