Messages in this thread | | | Subject | Re: [PATCH 21/21] tracing: Add optional percpu buffers for trace_printk() | From | Steven Rostedt <> | Date | Fri, 23 Sep 2011 07:16:45 -0400 |
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On Fri, 2011-09-23 at 13:07 +0200, Peter Zijlstra wrote: > 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? #$%@^%@@$%@
It is NMI safe, always was (I use it there too). It has a percpu recursion detection (always has), thus if an NMI interrupts a current trace_printk(), the NMI trace_printk() will not print. I could add an NMI buffer to allow NMIs to print, but so far, we don't usually have issues with trace_printk(). Heck, I'm not sure printk() wont cause issues in NMIs. I think trace_printk() is still safer than printk.
> > 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'.
Not, having per cpu buffers still doesn't allow NMIs to interrupt trace_printk(). Otherwise the NMI would just corrupt the current percpu buffer.
-- Steve
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