* Ingo Molnar <[email protected]> wrote:
> ah, you got the latency tracer from Thomas, as part of the -hrt patchset
> - that makes it quite a bit easier to debug. Could you run the attached
> trace-it-10sec utility:
>
> trace-it-10sec > trace-to-ingo.txt
attached ...
Ingo
/*
* Copyright (C) 2005, Ingo Molnar <[email protected]>
*
* user-triggered tracing.
*
* The -rt kernel has a built-in kernel tracer, which will trace
* all kernel function calls (and a couple of special events as well),
* by using a build-time gcc feature that instruments all kernel
* functions.
*
* The tracer is highly automated for a number of latency tracing purposes,
* but it can also be switched into 'user-triggered' mode, which is a
* half-automatic tracing mode where userspace apps start and stop the
* tracer. This file shows a dumb example how to turn user-triggered
* tracing on, and how to start/stop tracing. Note that if you do
* multiple start/stop sequences, the kernel will do a maximum search
* over their latencies, and will keep the trace of the largest latency
* in /proc/latency_trace. The maximums are also reported to the kernel
* log. (but can also be read from /proc/sys/kernel/preempt_max_latency)
*
* For the tracer to be activated, turn on CONFIG_WAKEUP_TIMING and
* CONFIG_LATENCY_TRACE in the .config, rebuild the kernel and boot
* into it. Note that the tracer can have significant runtime overhead,
* so you dont want to use it for performance testing :)
*/
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <sys/wait.h>
#include <linux/unistd.h>
int main (int argc, char **argv)
{
int ret;
if (getuid() != 0) {
fprintf(stderr, "needs to run as root.\n");
exit(1);
}
ret = system("cat /proc/sys/kernel/mcount_enabled >/dev/null 2>/dev/null");
if (ret) {
fprintf(stderr, "CONFIG_LATENCY_TRACING not enabled?\n");
exit(1);
}
// system("echo 0 > /proc/sys/kernel/trace_all_cpus");
system("echo 1 > /proc/sys/kernel/trace_enabled");
// system("echo 0 > /proc/sys/kernel/trace_freerunning");
system("echo 0 > /proc/sys/kernel/trace_print_at_crash");
system("echo 1 > /proc/sys/kernel/trace_user_triggered");
system("echo 0 > /proc/sys/kernel/trace_verbose");
system("echo 0 > /proc/sys/kernel/preempt_max_latency");
system("echo 0 > /proc/sys/kernel/preempt_thresh");
// system("[ -e /proc/sys/kernel/wakeup_timing ] && echo 1 > /proc/sys/kernel/wakeup_timing");
// system("echo 1 > /proc/sys/kernel/mcount_enabled");
prctl(0, 1); // start tracing
sleep(10);
prctl(0, 0); // stop tracing
system("cat /proc/latency_trace");
return 0;
}
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