Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753209Ab0LXEf3 (ORCPT ); Thu, 23 Dec 2010 23:35:29 -0500 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.124]:35892 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752601Ab0LXEf2 (ORCPT ); Thu, 23 Dec 2010 23:35:28 -0500 X-Authority-Analysis: v=1.1 cv=NFUeGz0loTdi/T6hXKngYYtckjed7x3pKvNOqmBBK18= c=1 sm=0 a=pPXw3_qIy5IA:10 a=Q9fys5e9bTEA:10 a=OPBmh+XkhLl+Enan7BmTLg==:17 a=meVymXHHAAAA:8 a=49WD_Y0i5dF8x-k797kA:9 a=ebJNC-J2ff51WBzfJkWLAYAPiuwA:4 a=PUjeQqilurYA:10 a=jeBq3FmKZ4MA:10 a=OPBmh+XkhLl+Enan7BmTLg==:117 X-Cloudmark-Score: 0 X-Originating-IP: 67.242.120.143 Subject: Re: ftrace: trace_pipe_raw interface broken From: Steven Rostedt To: David Sharp Cc: linux-kernel@vger.kernel.org, Michael Rubin In-Reply-To: References: <1292903569.22905.123.camel@gandalf.stny.rr.com> <1293119853.22802.33.camel@gandalf.stny.rr.com> Content-Type: text/plain; charset="ISO-8859-15" Date: Thu, 23 Dec 2010 23:35:26 -0500 Message-ID: <1293165326.22802.411.camel@gandalf.stny.rr.com> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1402 Lines: 40 On Thu, 2010-12-23 at 15:06 -0800, David Sharp wrote: > On Thu, Dec 23, 2010 at 7:57 AM, Steven Rostedt 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@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/