On Tue, 2010-06-08 at 18:22 +0200, Wolfgang Mauerer wrote:
> Philippe Gerum wrote:
> > On Tue, 2010-06-08 at 16:21 +0200, Wolfgang Mauerer wrote:
> >> Hi,
> >>
> >> the attached patch augments the timer expiration handler with some checks
> >> for excessive timer latencies. Depending on the configuration options, it
> >> freezes the ipipe tracer and creates a list of delayed timers.
> >>
> >> This code was useful for us in debugging some problems with faulty
> >> hardware.
> >> Would such a thing be suitable for mainline?
> >
> > No, I don't think so, albeit the debug feature it brings in makes sense.
> >
> > - the code, as is, adds significant cruft to the timer code, which is
> > per se a problem. Debug is ok, but I really would like that code to have
> > a much lower impact source-wise.
>
> so something along the lines of
>
> xntimer_enqueue_aperiodic(...)
> {
> ...
> large_latency_hook_whatever(args);
> ...
> }
>
> where large_latency_hook_whatever() is #ifdef'd to nop if not
> compile-time configured would be acceptable I suppose?
Yes.
>
> > - dependency on debugfs is wrong; we still have to take care of legacy
> > 2.4 kernels. I know, this is a real PITA, and I'm more than willing to
> > get rid of that "heritage" in 3.x, but for now, 2.x still requires to be
> > 2.4-compatible.
>
> oh, yeah. procfs would be a replacement, but using debugfs via ipipe
> is much nicer since this is definitely debugging stuff.
>
> > - but, beyond this, this is something that should go into the I-pipe
> > tracer instead, exporting a new dedicated interface to log a high
> > latency event. There, you could use whatever fits to implement it, since
> > there is by definition no consideration for compat with legacy kernels.
> > I'm thinking of having ipipe_trace_latency(unsigned long delta, const
> > char *source). That would be reusable in other, non-Xenomai contexts as
> > well.
>
> Sounds reasonable.
>
> Would it make sense to augment ipipe_trace_latency() with an additional
> type argument to distinguish different latency sources, or is this
> overkill?
>
It would even be required to store a latency event as a tracepoint in
the log, I guess, since we don't have room for any source label (which
would be overkill to have in every tracepoint anyway), but we do have a
type field there.
> Best, Wolfgang
>
> >
> > Additionally, the latency spots could appear as events in the tracer log
> > as well, which may help debugging them a lot, since you would know about
> > the actual context.
> >
> >> Regards, Wolfgang
> >>
> >> ---
> >> commit 9c2a3908ac4aff21022a577552002fc2622d3670
> >> Author: Wolfgang Mauerer <wolfgang.maue...@siemens.com>
> >> Date: Mon Jun 7 15:34:39 2010 +0200
> >>
> >> This patch provides the possibility to check upon timer expiration
> >> how much a timer has been delayed. When the delay surpasses a
> >> configurable
> >> threshold, the ipipe tracer is frozen. Additionally, the patch allows
> >> for the creation of a list of timers that have suffered from excessive
> >> delays.
> >>
> >> The mechanism can be disabled at both, compile- and runtime. There is
> >> no
> >> overhead in the former case.
> >>
> >> Signed-off-by: Wolfgang Mauerer <wolfgang.maue...@siemens.com>
> >>
> >> diff --git a/ksrc/nucleus/Kconfig b/ksrc/nucleus/Kconfig
> >> index 211a4ad..ffed3f8 100644
> >> --- a/ksrc/nucleus/Kconfig
> >> +++ b/ksrc/nucleus/Kconfig
> >> @@ -293,6 +293,24 @@ config XENO_OPT_DEBUG_TIMERS
> >> This option activates debugging output for critical
> >> timer-related operations performed by the Xenomai core.
> >>
> >> +config XENO_OPT_DEBUG_TIMER_LATENCY
> >> + bool "Log excessive timer latencies"
> >> + depends on XENO_OPT_DEBUG && (XENO_OPT_STATS || IPIPE_TRACE)
> >> + help
> >> +
> >> + This option activates recording of excessive timer latencies.
> >> + In contrast to the userland latency checker which is statistical
> >> + in nature, this test checks every expiring timer and is thus
> >> + more precise. However, it adds some runtime overhead when
> >> + activated.
> >> +
> >> + When the ipipe tracer is enabled, the trace is frozen
> >> + when a latency maximum above the threshold set in
> >> + the debugfs file timer_lattest/lat_threshold_us is detected.
> >> + When Xenomai statistics collection is enabled, a list of
> >> + excessive latencies together with the names of the timers
> >> + is kept in the debugfs file timer_lattest/exc_timer_list.
> >> +
> >> config XENO_OPT_DEBUG_SYNCH_RELAX
> >> bool "Detect mutexes held in relaxed sections"
> >> depends on XENO_OPT_PERVASIVE && XENO_OPT_DEBUG
> >> diff --git a/ksrc/nucleus/timer.c b/ksrc/nucleus/timer.c
> >> index d813c4f..01dad44 100644
> >> --- a/ksrc/nucleus/timer.c
> >> +++ b/ksrc/nucleus/timer.c
> >> @@ -36,11 +36,37 @@
> >> *
> >> *...@{*/
> >>
> >> +#include <linux/debugfs.h>
> >> #include <nucleus/pod.h>
> >> #include <nucleus/thread.h>
> >> #include <nucleus/timer.h>
> >> +#include <nucleus/trace.h>
> >> #include <asm/xenomai/bits/timer.h>
> >>
> >> +#ifdef CONFIG_XENO_OPT_DEBUG_TIMER_LATENCY
> >> +#define NANO 1000000000ll
> >> +#define MU 1000000ll
> >> +#define NANO_PER_MU (NANO/MU)
> >> +
> >> +static u32 lat_thresh = 0; /* in \mu s, set to zero to disable */
> >> +
> >> +#ifdef CONFIG_XENO_OPT_STATS
> >> +#include <linux/seq_file.h>
> >> +
> >> +#define NUM_REC_LATENCIES 500
> >> +static int num_lat_exc_timers = -1;
> >> +static bool lat_rec_overflow = false; /* Set when more than
> >> NUM_REC_LATENCIES
> >> + * excessive latencies have been
> >> + * observed */
> >> +struct lat_rec {
> >> + char name[XNOBJECT_NAME_LEN];
> >> + xnsticks_t delta;
> >> +};
> >> +
> >> +static struct lat_rec delayed_timers[NUM_REC_LATENCIES];
> >> +#endif // CONFIG_XENO_OPT_STATS
> >> +#endif // XENO_OPT_DEBUG_TIMER_LATENCY
> >> +
> >> static inline void xntimer_enqueue_aperiodic(xntimer_t *timer)
> >> {
> >> xntimerq_t *q = &timer->sched->timerqueue;
> >> @@ -368,6 +394,32 @@ void xntimer_tick_aperiodic(void)
> >> if (delta > (xnsticks_t)nklatency)
> >> break;
> >>
> >> +#ifdef CONFIG_XENO_OPT_DEBUG_TIMER_LATENCY
> >> + /*
> >> + * Check for severly delayed timers, but omit the host tick
> >> + * timer as it can be delayed intentionally, thus causing
> >> + * spurious excessive latencies (see
> >> + * xntimer_next_local_shot()).
> >> + */
> >> + if (lat_thresh && (timer != &sched->htimer)) {
> >> + delta = xnarch_tsc_to_ns(-delta);
> >> + if (delta > ((xnsticks_t)lat_thresh)*NANO_PER_MU) {
> >> + xnarch_trace_user_freeze(delta, 1);
> >> +#ifdef CONFIG_XENO_OPT_STATS
> >> + if (num_lat_exc_timers < NUM_REC_LATENCIES - 1)
> >> {
> >> + num_lat_exc_timers++;
> >> + } else {
> >> + lat_rec_overflow = true;
> >> + num_lat_exc_timers = 0;
> >> + }
> >> +
> >> xnobject_copy_name(delayed_timers[num_lat_exc_timers].name,
> >> + timer->name);
> >> + delayed_timers[num_lat_exc_timers].delta =
> >> delta;
> >> +#endif // XENO_OPT_STATS
> >> + }
> >> + }
> >> +#endif // XENO_OPT_DEBUG_TIMER_LATENCY
> >> +
> >> trace_mark(xn_nucleus, timer_expire, "timer %p", timer);
> >>
> >> xntimer_dequeue_aperiodic(timer);
> >> @@ -1147,10 +1199,70 @@ static int timer_read_proc(char *page,
> >> return len;
> >> }
> >>
> >> +#ifdef CONFIG_XENO_OPT_STATS
> >> +static int lat_exc_seq_show(struct seq_file *f, void *v)
> >> +{
> >> + int count, max;
> >> +
> >> + if (num_lat_exc_timers < 0) {
> >> + seq_printf(f, "(No excessive timer latencies detected)\n");
> >> + return 0;
> >> + }
> >> +
> >> + if (lat_rec_overflow)
> >> + max = NUM_REC_LATENCIES;
> >> + else
> >> + max = num_lat_exc_timers;
> >> +
> >> + for (count = 0; count < max; count++) {
> >> + seq_printf(f, "Timer '%s', delay %lld ns\n",
> >> + delayed_timers[count].name,
> >> + delayed_timers[count].delta);
> >> + }
> >> +
> >> + if (lat_rec_overflow) {
> >> + seq_printf(f, "WARNING: Latency tracking array overflow
> >> detected.\n");
> >> + seq_printf(f, " Not all excessive latencies are
> >> shown.\n");
> >> +
> >> + }
> >> + return 0;
> >> +}
> >> +
> >> +static int lat_exc_seq_open(struct inode *inode, struct file *file)
> >> +{
> >> + return single_open(file, lat_exc_seq_show, NULL);
> >> +}
> >> +
> >> +static struct file_operations lat_exc_fops = {
> >> + .owner = THIS_MODULE,
> >> + .open = lat_exc_seq_open,
> >> + .read = seq_read,
> >> + .llseek = seq_lseek,
> >> +};
> >> +#endif // CONFIG_XENO_OPT_STATS
> >> +
> >> void xntimer_init_proc(void)
> >> {
> >> rthal_add_proc_leaf("timer", &timer_read_proc, NULL, NULL,
> >> rthal_proc_root);
> >> +
> >> +#ifdef CONFIG_XENO_OPT_DEBUG_TIMER_LATENCY
> >> + struct dentry *debugfs_dir;
> >> +
> >> + debugfs_dir = debugfs_create_dir("timer_lattest", NULL);
> >> +
> >> + if (debugfs_dir) {
> >> + if (!debugfs_create_u32("lat_threshold_us", 0666,
> >> + debugfs_dir, &lat_thresh))
> >> + panic("Could not create lat_threshold_us");
> >> +
> >> +#ifdef CONFIG_XENO_OPT_STATS
> >> + if (!debugfs_create_file("exc_timer_list", 0600,
> >> + debugfs_dir, NULL, &lat_exc_fops))
> >> + panic("Could not create exc_timer_list");
> >> +#endif // XENO_OPT_STATS
> >> + }
> >> +#endif // XENO_OPT_DEBUG_TIMER_LATENCY
> >> }
> >>
> >> void xntimer_cleanup_proc(void)
> >>
> >> _______________________________________________
> >> Xenomai-core mailing list
> >> Xenomai-core@gna.org
> >> https://mail.gna.org/listinfo/xenomai-core
> >
> >
>
--
Philippe.
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