* Steven Noonan <steven@xxxxxxxxxxxxxx> wrote: > On Fri, Sep 19, 2008 at 1:22 AM, Steven Noonan <steven@xxxxxxxxxxxxxx> wrote: > > On Fri, Sep 19, 2008 at 1:17 AM, Ingo Molnar <mingo@xxxxxxx> 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. yeah, had the same thought. Could you please contribute one? :) I'd suggest you take the smallest tracer as a template: trace_sched_switch.c and turn that into trace_nop.c - and change all the function names and ASCII and kconfig glue to 'nop'/'NOP'? That can then be used as a basis for additional ftrace plugins, or for ad-hoc temporary tracing. Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
