linux-kernel - Re: [ath9k-devel] ath9k: massive unexplained latency in 2.6.27 (rc5, rc6, probably others)

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Message-ID: <f488382f0809190145s1b5407d4s9d97ae594bcc3379@mail.gmail.com>
Date:	Fri, 19 Sep 2008 01:45:11 -0700
From:	"Steven Noonan" <steven@...inklabs.net>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Luis R. Rodriguez" <lrodriguez@...eros.com>,
	"Luis Rodriguez" <Luis.Rodriguez@...eros.com>,
	"ath9k-devel@...ts.ath9k.org" <ath9k-devel@...ts.ath9k.org>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [ath9k-devel] ath9k: massive unexplained latency in 2.6.27 (rc5, rc6, probably others)

On Fri, Sep 19, 2008 at 1:22 AM, Steven Noonan <steven@...inklabs.net> wrote:
> On Fri, Sep 19, 2008 at 1:17 AM, Ingo Molnar <mingo@...e.hu> 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.
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