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

Steven Noonan
2008-09-19T08:45:29Z

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