From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754173AbYKBQwS (ORCPT ); Sun, 2 Nov 2008 11:52:18 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753688AbYKBQwG (ORCPT ); Sun, 2 Nov 2008 11:52:06 -0500 Received: from qw-out-2122.google.com ([74.125.92.25]:62957 "EHLO qw-out-2122.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753681AbYKBQwE (ORCPT ); Sun, 2 Nov 2008 11:52:04 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version :content-type:content-transfer-encoding:content-disposition :references; b=kFm9AK1oOWF02WQlxFEeVm/jJcN9f+czXHMNVtXcvnVgrP+JGeRQXeoitGc4v22yH4 Nm9Pb2YDauiCVTUn+rv0PapZC3Bey7Rd6p0bZGeFhXm2u9xhmThFHX3Io3NQMev5tHft ulukVa5gDjc4+6uy+ZGD2Aknkc42venD5C5Y4= Message-ID: Date: Sun, 2 Nov 2008 17:52:02 +0100 From: "=?ISO-8859-1?Q?Fr=E9d=E9ric_Weisbecker?=" To: "Pekka Paalanen" Subject: Re: Tracing framework regressions in 2.6.28-rc2 Cc: "Steven Rostedt" , linux-kernel , "Ingo Molnar" In-Reply-To: <20081102183534.1bdc6779@daedalus.pq.iki.fi> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <20081102183534.1bdc6779@daedalus.pq.iki.fi> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Pekka! 2008/11/2 Pekka Paalanen : > Hi all, > > I finally had the time to check how mmiotrace works in 2.6.28-rc2. > On the first try I didn't find any mmiotrace problems, I traced the > Nouveau DRM driver just fine, but the file /debug/tracing/current_tracer > has started to misbehave. > > I think it is due to this patch: > > commit c2931e05ec5965597cbfb79ad332d4a29aeceb23 > Author: Frederic Weisbecker > Date: Sat Oct 4 22:04:44 2008 +0200 > > ftrace: return an error when setting a nonexistent tracer > > When one try to set a nonexistent tracer, no error is returned > as if the name of the tracer was correct. > We should return -EINVAL. > > Signed-off-by: Frederic Weisbecker > Acked-by: Steven Rostedt > Signed-off-by: Ingo Molnar > > Now, whatever I echo to current_tracer, I get EINVAL. > What's more confusing, if I do > echo mmiotrace > /debug/tracing/current_tracer > then I see the EINVAL error *and* mmiotrace is activated! > > The problem is with newlines, with 'echo -n' it works as it should. > > I'm starting to think the patch itself is fine, but it exposes an > assumption in the write fop: a single write call contains all the > data. I suspect there are actually two write calls in case of 'echo': > one with 'mmiotrace' and one with '\n'. I don't see how else I could > get the behaviour I get. A patch has been applied for this in the mainline, the issue will be fixed for rc3: http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=60063a66236c15f5613f91390631e06718689782 > Another issue is the disappeared 'none' pseudo-tracer, which seems > to be replaced with the 'nop' real tracer. Is using 'nop' now equivalent > to the previous 'none' tracer? Yes. A nop tracer has been released to have a kind of pattern to write new tracers, and to have a tracer that does nothing but is able to show user marks for example. Since it does nothing, we replaced the none tracer by this one. > I mean, when the 'nop' tracer is current, are all tracing calls no-ops and > nothing will ever get into the ring buffer? > I have to update the mmiotrace documentation about disabling tracing. Hhm not really, you can receive pseudo entries like user marks. But you can disable all the tracing by setting 0 to tracing_enabled.