From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755975AbYIOTrY (ORCPT ); Mon, 15 Sep 2008 15:47:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753503AbYIOTrQ (ORCPT ); Mon, 15 Sep 2008 15:47:16 -0400 Received: from ik-out-1112.google.com ([66.249.90.182]:11759 "EHLO ik-out-1112.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753352AbYIOTrP (ORCPT ); Mon, 15 Sep 2008 15:47:15 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:in-reply-to:references:x-mailer :mime-version:content-type:content-transfer-encoding:sender; b=feieFPG7Fecj1493lU1qag8oMvJjbQk9QXQ13I3TpriqVatnMrpafljVNgBVgO8EjA JYX6me/E+S103PZBgQY6MwefE+YLF6dTDocOSMr6qah6R5hCaDwGNPqxzudFRWc849jI +K0PHmccrHsbj/wUf4w24XcjoiyRj04/ZYF60= Date: Mon, 15 Sep 2008 22:47:07 +0300 From: Pekka Paalanen To: Steven Rostedt Cc: =?ISO-8859-1?Q?Fr=E9d=E9ric?= Weisbecker , Ingo Molnar , Linux Kernel Subject: Tracing/ftrace: trouble with trace_entries and trace_pipe Message-ID: <20080915224707.76b2cca0@daedalus.pq.iki.fi> In-Reply-To: References: <48B1D5CA.8000607@gmail.com> <20080827212130.4b8365a8@daedalus.pq.iki.fi> <20080828214256.296e34ec@daedalus.pq.iki.fi> <20080904203058.7e57729e@daedalus.pq.iki.fi> X-Mailer: Claws Mail 3.5.0 (GTK+ 2.12.11; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Steven and others, first a minor bug: it seems the units of /debug/tracing/trace_entries is different for read and write. This is confusing for the users, since I can't say "if you have problems, double it". If I read from it something like 16422, then write back 16422, next I read 214. I can't recall the exact numbers, but the difference really is two orders of magnitude. I have 1 GB RAM in this box, so that shouldn't be an issue. My other problem is with trace_pipe. It is again making 'cat' quit too early. The condition triggered is if (!tracer_enabled && iter->pos) { in tracing_read_pipe(), and it is followed by triggering /* stop when tracing is finished */ if (trace_empty(iter)) { and then sret=0, so read returns 0 and 'cat' exits. Now, I am trying my mmiotrace marker patches, but as far as I can tell, nothing I modified is the reason for this. I didn't yet explicitly test for it, though. I'll send these patches after I hear from Frederic. The cat-quit problem is not a constant state. After boot, I could play with my markers and testmmiotrace without cat quitting. Then something happens, and cat starts the quitting behaviour, and won't get to normal by disabling and enabling mmiotrace. I have a couple of wild guesses of what might be related: - ring buffer wrap-around - ring buffer overflow (at first try I hit these, the second try after putting debug-pr_info's in place I don't hit this) - ring buffer resize (after playing with trace_entries, cat-quit problem was present, though it might have been present before) After viewing the git history, I have some more guesses, mainly related to setting tracer_enabled to 0. - commit 2b1bce1787700768cbc87c8509851c6f49d252dc I don't see where tracer_enabled would be set to 1, when mmiotrace is enabled. It used to default to 1 and mmiotrace was happy. - __tracing_open() sets it to 0 (not called for the pipe) - tracing_release() sets it to 1 - tracing_ctrl_write() toggles it - tracing_read_pipe() tests it - tracer_alloc_buffers() uses it And other tracers seem to use it a lot. Mmiotrace does use the tracer::ctrl_update hook, and allow/disallow calls to __trace_mmiotrace_{rw,map}() via enabling/disabling the whole mmiotrace core. Is this not enough, or is it inappropriate? It seems tracer_enabled is used by the trace framework itself to enable/disable... what? Hmm, maybe nothing I care about. Should mmiotrace simply do tracer_enabled = 1; in mmio_trace_init()? Should mmiotrace test tracer_enabled, and if so, when? Thanks. -- Pekka Paalanen http://www.iki.fi/pq/