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Date: Thu, 1 Jun 2017 20:47:35 -0400 From: Steven Rostedt <rostedt@...dmis.org> To: Peter Zijlstra <peterz@...radead.org> Cc: Vlastimil Babka <vbabka@...e.cz>, Lu Baolu <baolu.lu@...ux.intel.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Ingo Molnar <mingo@...hat.com>, Mathias Nyman <mathias.nyman@...ux.intel.com>, tglx@...utronix.de, linux-usb@...r.kernel.org, x86@...nel.org, linux-kernel@...r.kernel.org, Michal Kubecek <mkubecek@...e.cz> Subject: Re: [PATCH v8 2/5] usb: early: add driver for xhci debug capability On Thu, 1 Jun 2017 14:25:51 +0200 Peter Zijlstra <peterz@...radead.org> wrote: > On Thu, Jun 01, 2017 at 10:15:24AM +0200, Vlastimil Babka wrote: > > Thanks. I didn't make it clear that the trace_printk() warning is > > there even if the code using it doesn't actually execute (i.e. I > > didn't specify any early_printk bootparam). There are some roastedy > > tricks to detect the potential users, so that the buffers can be > > allocated in advance to allow the first trace_printk() from any > > context, I guess. > > > > I'm not sure if there's a way to change it so that your driver > > reports the trace_printk usage only in response to the bootparam > > (which could also be a safe point to allocate ftrace buffers?). > > No, nor do we want to. There should not be a single caller to > trace_printk() in normal kernels. Correct. If you find a trace_printk() that would be useful in a production environment, then make it a tracepoint. That's why I have that nasty banner, to make sure trace_printk()s are not the "quick way" to add tracepoint hacks. -- Steve
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