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Date: Thu, 23 Dec 2010 23:35:26 -0500 From: Steven Rostedt <rostedt@...dmis.org> To: David Sharp <dhsharp@...gle.com> Cc: linux-kernel@...r.kernel.org, Michael Rubin <mrubin@...gle.com> Subject: Re: ftrace: trace_pipe_raw interface broken On Thu, 2010-12-23 at 15:06 -0800, David Sharp wrote: > On Thu, Dec 23, 2010 at 7:57 AM, Steven Rostedt <rostedt@...dmis.org> wrote: > > Not quite intended, but not something to worry about either. We mask off > > the 30 bits to determine the size. > > in trace-cmd you mean? Yeah, but if you find that strange, I guess we could mask it off too. > > >> By my count that leaves only one mystery: why are we seeing this extra > >> page at the beginning with pre-overflow data? > > > > If you did not reset the buffer, there's a chance that the writer is on > > the reader page. The reader page is always outside the ring buffer, but > > it points into the ring buffer. If this occurs, then you will get the > > reader page data, plus the rest of the ring buffer (which is the full > > size you asked for). > > Okay, that's a surprising behavior to me, but resetting the buffer > seems like a fine workaround. Getting a little more trace than you asked for seems like a good thing to me ;-) > > btw, corroborating this is that reading the formatted output of > "trace" also shows the page of pre-overflow data. Yep, that's already known. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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