From: Steven Rostedt The irqsoff tracer will fail to swap the cpu buffer with the max buffer if it preempts a commit. Instead of ignoring this, this patch makes the tracer report it if the last max latency failed due to preempting a current commit. The output of the latency tracer will look like this: # tracer: irqsoff # # irqsoff latency trace v1.1.5 on 2.6.31-rc5 # -------------------------------------------------------------------- # latency: 112 us, #1/1, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) # ----------------- # | task: -4281 (uid:0 nice:0 policy:0 rt_prio:0) # ----------------- # => started at: save_args # => ended at: __do_softirq # # # _------=> CPU# # / _-----=> irqs-off # | / _----=> need-resched # || / _---=> hardirq/softirq # ||| / _--=> preempt-depth # |||| / # ||||| delay # cmd pid ||||| time | caller # \ / ||||| \ | / bash-4281 1d.s6 265us : update_max_tr_single: Failed to swap buffers due to commit in progress Note the latency time and the functions that disabled the irqs or preemption will still be listed. Signed-off-by: Steven Rostedt --- kernel/trace/trace.c | 13 ++++++++++++- 1 files changed, 12 insertions(+), 1 deletions(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index ef08328..6df9861 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -482,9 +482,20 @@ update_max_tr_single(struct trace_array *tr, struct task_struct *tsk, int cpu) ret = ring_buffer_swap_cpu(max_tr.buffer, tr->buffer, cpu); + if (ret == -EBUSY) { + /* + * We failed to swap the buffer due to a commit taking + * place on this CPU. We fail to record, but we reset + * the max trace buffer (no one writes directly to it) + * and flag that it failed. + */ + trace_array_printk(&max_tr, _THIS_IP_, + "Failed to swap buffers due to commit in progress\n"); + } + ftrace_enable_cpu(); - WARN_ON_ONCE(ret && ret != -EAGAIN); + WARN_ON_ONCE(ret && ret != -EAGAIN && ret != -EBUSY); __update_max_tr(tr, tsk, cpu); __raw_spin_unlock(&ftrace_max_lock); -- 1.6.3.3 -- -- 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/