* Serge Noiraud <[email protected]> wrote:
> > and start a new search for a maximum latency via:
> >
> > echo 0 > /proc/sys/kernel/preempt_max_latency
> >
> > and then do the X test - what is the largest latency reported in
> > 'dmesg'? Also, please send me a (bzip2 -9 compressed, if too large)
> > /proc/latency_trace trace output of the largest incident.
> The max latency reported are normal.
yeah. (btw., enable CONFIG_KALLSYMS to get a much more readable trace
output)
> I have the problem with another program which mesure latencies about
> semaphore only in X environment too.
>
> I tried to ssh this machine from another X environment and the problem
> does not exist. It's only on the console.
does your measurement program do any tty IO during the measurement? That
could delay the measurement code artificially. Generally, latency
measurement must be done very carefully (userspace and kernelspace
alike).
E.g. rtc_wakeup uses a FIFO between two threads to isolate the
measurement thread as much as possible. rtc_wakeup can be found at:
http://www.affenbande.org/~tapas/wiki/index.php?rtc_wakeup
and should be run like:
chrt -f 95 -p `pidof 'IRQ 8'`
./rtc_wakeup -f 1024 -t 100000
if you only trust your own measurement code then you can use a hybrid
tracing method as well: switch the kernel's trace into 'user triggered':
echo 1 > /proc/sys/kernel/trace_user_triggered
then you can turn tracing on in your code via a syscall hack:
gettimeofday(0,1);
(yes - gettimeofday. Has nothing to do with tracing.) You can turn
tracing off via:
gettimeofday(0,0);
and the kernel will do a maximum search for you, and you should have the
highest-latency trace available in /proc/latency_trace.
Ingo
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
