Return-path: Received: from qb-out-0506.google.com ([72.14.204.226]:49298 "EHLO qb-out-0506.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750960AbYISIpP (ORCPT ); Fri, 19 Sep 2008 04:45:15 -0400 Received: by qb-out-0506.google.com with SMTP id f11so263278qba.17 for ; Fri, 19 Sep 2008 01:45:12 -0700 (PDT) Message-ID: (sfid-20080919_104521_745577_F6431BA5) Date: Fri, 19 Sep 2008 01:45:11 -0700 From: "Steven Noonan" To: "Ingo Molnar" Subject: Re: [ath9k-devel] ath9k: massive unexplained latency in 2.6.27 (rc5, rc6, probably others) Cc: "Luis R. Rodriguez" , "Luis Rodriguez" , "ath9k-devel@lists.ath9k.org" , linux-wireless , LKML In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 References: <20080918220102.GE7408@tesla> <43e72e890809181508w5232a14ewbf2bf18fe90a92d5@mail.gmail.com> <43e72e890809181610h3a7729d8s4c8484d97b21932e@mail.gmail.com> <20080919030125.GG7408@tesla> <20080919081733.GC19491@elte.hu> Sender: linux-wireless-owner@vger.kernel.org List-ID: On Fri, Sep 19, 2008 at 1:22 AM, Steven Noonan wrote: > On Fri, Sep 19, 2008 at 1:17 AM, Ingo Molnar wrote: >> in tip/master there's an ftrace_printk() facility. You can just replace >> the verbose printk()s with ftrace_printk() and see the result in >> /debug/tracing/trace. >> >> This sort of tracing has very low overhead and can be used in an easy >> ad-hoc manner with no extra infrastructure. Here's a few quick-start >> links about how to enable the scheduler tracer: >> >> http://redhat.com/~mingo/sched-devel.git/readme-tracer.txt >> http://redhat.com/~mingo/sched-devel.git/howto-trace-latencies.txt >> >> any ftrace_printk() you add in the kernel will show up in that trace. >> >> (If the scheduling events are uninteresting and clutter the output then >> you might want to remove the scheduler tracing entries from kernel/*.c >> by removing the trace_sched_*() calls or use a less noisy tracer.) >> >> to get enough of a trace history you might want to increase the number >> of trace entries in /debug/tracing/trace_entries from 16K to 128K or so. >> > > Thanks for the suggestion, I'll do that. :) > It'd be extremely convenient to have a tracer that did absolutely nothing but display ftrace_printk()s.