* Miklos Szeredi <mik...@szeredi.hu> wrote:
> On Fri, 20 Mar 2009, Peter Zijlstra wrote:
> > On Thu, 2009-03-19 at 23:23 +0100, Miklos Szeredi wrote:
> > >
> > > This patch solves this by not scheduling on preempt_enable() after
> > > ptrace_stop() has woken up the tracer.
> >
> > Nice,.. however did you find this?
>
> Ftrace helped a lot, it's a really cool tool :). I had to patch it
> with this, otherwise the timestamps would be totally off:
>
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index bd38c5c..557c2dd 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -108,7 +108,7 @@ u64 ring_buffer_time_stamp(int cpu)
>
> preempt_disable_notrace();
> /* shift to debug/test normalization and TIME_EXTENTS */
> - time = sched_clock() << DEBUG_SHIFT;
> + time = cpu_clock(cpu) << DEBUG_SHIFT;
> preempt_enable_no_resched_notrace();
Btw., based on your earlier report, the same is now possible in the
latest tracing tree via:
echo 1 > /debug/tracing/options/global_clock
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