Re: [PATCH 21/21] tracing: Add optional percpu buffers for trace_printk()

Peter Zijlstra
2011-09-23T11:07:43Z

On Fri, 2011-09-23 at 13:02 +0200, Peter Zijlstra wrote:
> On Thu, 2011-09-22 at 18:09 -0400, Steven Rostedt wrote:
> >
> > Currently, trace_printk() uses a single buffer to write into
> > to calculate the size and format needed to save the trace. To
> > do this safely in an SMP environment, a spin_lock() is taken
> > to only allow one writer at a time to the buffer. But this could
> > also affect what is being traced, and add synchronization that
> > would not be there otherwise.
>
> so trace_printk() isn't NMI safe? #$%@^%@@$%@

better to make all of trace_printk() depend on that extra config, there
is absolutely 0 point in having a broken and fully serialized trace
'fail^wfeature'.