From 2f26ebd549b9ab55ac756b836ec759c11fe93f81 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Tue, 1 Sep 2009 11:06:29 -0400 Subject: tracing: use timestamp to determine start of latency traces Currently the latency tracers reset the ring buffer. Unfortunately if a commit is in process (due to a trace event), this can corrupt the ring buffer. When this happens, the ring buffer will detect the corruption and then permanently disable the ring buffer. The bug does not crash the system, but it does prevent further tracing after the bug is hit. Instead of reseting the trace buffers, the timestamp of the start of the trace is used instead. The buffers will still contain the previous data, but the output will not count any data that is before the timestamp of the trace. Note, this only affects the static trace output (trace) and not the runtime trace output (trace_pipe). The runtime trace output does not make sense for the latency tracers anyway. Reported-by: Arnaldo Carvalho de Melo Signed-off-by: Steven Rostedt --- kernel/trace/trace_irqsoff.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) (limited to 'kernel/trace/trace_irqsoff.c') diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c index b923d13e2fad..5555b75a0d12 100644 --- a/kernel/trace/trace_irqsoff.c +++ b/kernel/trace/trace_irqsoff.c @@ -178,7 +178,6 @@ out_unlock: out: data->critical_sequence = max_sequence; data->preempt_timestamp = ftrace_now(cpu); - tracing_reset(tr, cpu); trace_function(tr, CALLER_ADDR0, parent_ip, flags, pc); } @@ -208,7 +207,6 @@ start_critical_timing(unsigned long ip, unsigned long parent_ip) data->critical_sequence = max_sequence; data->preempt_timestamp = ftrace_now(cpu); data->critical_start = parent_ip ? : ip; - tracing_reset(tr, cpu); local_save_flags(flags); @@ -379,6 +377,7 @@ static void __irqsoff_tracer_init(struct trace_array *tr) irqsoff_trace = tr; /* make sure that the tracer is visible */ smp_wmb(); + tracing_reset_online_cpus(tr); start_irqsoff_tracer(tr); } -- cgit v1.2.2 From 41dfba4367109b92d92ec6e059be6950497d932f Mon Sep 17 00:00:00 2001 From: Carsten Emde Date: Sun, 13 Sep 2009 01:41:31 +0200 Subject: tracing: remove unused local variables in tracer probe functions When the nsecs_to_usecs() conversion in probe_wakeup_sched_switch() and check_critical_timing() was moved to a later stage in order to avoid unnecessary computing, it was overlooked to remove the original variables, assignments and comments.. Signed-off-by: Carsten Emde Signed-off-by: Steven Rostedt --- kernel/trace/trace_irqsoff.c | 12 +----------- 1 file changed, 1 insertion(+), 11 deletions(-) (limited to 'kernel/trace/trace_irqsoff.c') diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c index 5555b75a0d12..06f8ea9e4b9d 100644 --- a/kernel/trace/trace_irqsoff.c +++ b/kernel/trace/trace_irqsoff.c @@ -129,15 +129,10 @@ check_critical_timing(struct trace_array *tr, unsigned long parent_ip, int cpu) { - unsigned long latency, t0, t1; cycle_t T0, T1, delta; unsigned long flags; int pc; - /* - * usecs conversion is slow so we try to delay the conversion - * as long as possible: - */ T0 = data->preempt_timestamp; T1 = ftrace_now(cpu); delta = T1-T0; @@ -157,17 +152,12 @@ check_critical_timing(struct trace_array *tr, trace_function(tr, CALLER_ADDR0, parent_ip, flags, pc); - latency = nsecs_to_usecs(delta); - if (data->critical_sequence != max_sequence) goto out_unlock; - tracing_max_latency = delta; - t0 = nsecs_to_usecs(T0); - t1 = nsecs_to_usecs(T1); - data->critical_end = parent_ip; + tracing_max_latency = delta; update_max_tr_single(tr, current, cpu); max_sequence++; -- cgit v1.2.2 From b5130b1e7d3717d03ab1916b198bf0d49fa0a619 Mon Sep 17 00:00:00 2001 From: Carsten Emde Date: Sun, 13 Sep 2009 01:43:07 +0200 Subject: tracing: do not update tracing_max_latency when tracer is stopped The state of the function pair tracing_stop()/tracing_start() is correctly considered when tracer data are updated. However, the global and externally accessible variable tracing_max_latency is always updated - even when tracing is stopped. The update should only occur, if tracing was not stopped. Signed-off-by: Carsten Emde Signed-off-by: Steven Rostedt --- kernel/trace/trace_irqsoff.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) (limited to 'kernel/trace/trace_irqsoff.c') diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c index 06f8ea9e4b9d..3aa7eaa2114c 100644 --- a/kernel/trace/trace_irqsoff.c +++ b/kernel/trace/trace_irqsoff.c @@ -157,8 +157,10 @@ check_critical_timing(struct trace_array *tr, data->critical_end = parent_ip; - tracing_max_latency = delta; - update_max_tr_single(tr, current, cpu); + if (likely(!is_tracing_stopped())) { + tracing_max_latency = delta; + update_max_tr_single(tr, current, cpu); + } max_sequence++; -- cgit v1.2.2