Messages in this thread | | | Date | Thu, 28 May 2009 16:52:39 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH] tracing: annotate emit_log_char() notrace |
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On Thu, 28 May 2009, Frederic Weisbecker wrote: > On Wed, May 27, 2009 at 05:00:44PM +0200, Thomas Gleixner wrote: > > printk calls emit_log_char() in a loop which is cluttering the trace > > buffer. Make it notrace. > > > > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > > --- > > > Does it produce that much annoying traces? > I mean, printk() are usually rare events. > > Do you have a particular debugging workflow that makes this > function invasive in the trace? > > May be it's because you are debugging using ftrace and other > debugging options that use a lot of printk() > In such case, it would indeed be good to apply this patch.
I noticed when I chased a boot up problem, half of the trace was full of
0.540550: emit_log_char <-vprintk 0.540550: emit_log_char <-vprintk ...
though there is another annoyance in the same code path:
0.540557: vgacon_set_cursor_size <-vgacon_cursor 0.540558: __rcu_read_lock <-__atomic_notifier_call_chain 0.540558: __rcu_read_unlock <-__atomic_notifier_call_chain 0.540558: __rcu_read_lock <-__atomic_notifier_call_chain ...
It's actually the same number of times as we have emit_log_char() there. __atomic_notifier_call_chain() itself is marked notrace but the rcu calls inside are not. :(
IIRC the same happens with a serial console, but that can be worse as you busy wait during the character output.
It'd be nice if we could inherit the notrace from the caller :)
Thanks,
tglx
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