On 9/22/07, Arnaldo Carvalho de Melo <acme@xxxxxxxxxxxxxxxxxx> wrote:
> Em Sat, Sep 22, 2007 at 02:22:00PM -0400, Cliff Brake escreveu:
> > I have a system where I am doing the following on a PXA270 ARM system:
> >
> > An applications is sending and receiving a packet on a serial port
> > every 40ms. With 2.6.20, I simply enabled kernel preemption and set
> > the priority of my application to real-time, and it worked great, no
> > matter what the system load.
>
> You didn't made it clear what exactly is the kernel version you are
> using. You mention 2.6.20, but is this with or without the PREEMPT_RT
> patch?
without the PREEMPT_RT patch -- just using the mainline PREEMPT support.
> > With 2.6.23-rc6, I have enabled CONFIG_HIGH_RES_TIMERS &
> > CONFIG_PREEMPT. Scheduling in the real-time application is rock solid
> > and looking at timing with a scope, and instrumenting the loop in the
> > application indicates the 40ms is very solid. However, it seems the
> > receive data is getting stuck in the serial driver for relatively long
> > periods of time (>= 40ms), which is a problem in this system.
> >
> > Is there anything that would have changed between 2.6.20 and
> > 2.6.23-rc6 that would explain this? What priority do pieces of the
> > serial driver run at? Is there any way to make the serial driver run
> > at high priority so that data is processed in a timely manner?
>
> Look at the IRQ-<N> kernel thread that services the serial port hardware
> interrupt, use chrt to bump its priority and see if it helps.
I don't see any IRQ-<N> processes on my system -- does this require
the RT patch? Perhaps this is different on ARM/x86?
Thanks,
Cliff
root@compulab-pxa270:~$ ps -A
PID TTY TIME CMD
1 ? 00:00:02 init
2 ? 00:00:00 kthreadd
3 ? 00:00:00 ksoftirqd/0
4 ? 00:00:03 events/0
5 ? 00:00:00 khelper
46 ? 00:00:00 kblockd/0
56 ? 00:00:00 khubd
59 ? 00:00:00 kseriod
82 ? 00:00:00 pdflush
83 ? 00:00:00 pdflush
84 ? 00:00:00 kswapd0
85 ? 00:00:00 aio/0
194 ? 00:00:00 mtdblockd
240 ? 00:00:00 kpsmoused
397 ? 00:00:00 udevd
1221 ? 00:00:00 power
1238 ? 00:00:15 jffs2_gcd_mtd4
1271 ? 00:00:00 kmmcd
1278 ? 00:00:00 pegasus
1288 ? 00:00:01 mmcqd
1433 ? 00:00:00 kjournald
1497 ? 00:00:00 portmap
1551 ? 00:00:00 dropbear
1565 ? 00:00:00 dbus-daemon
1571 ? 00:00:00 syslogd
1573 ? 00:00:00 klogd
1582 ? 00:00:00 avahi-daemon
1630 tty2 00:02:55 Xfbdev
1633 ttyS0 00:11:23 svs
1649 tty1 00:00:00 sh
1668 ttyS0 00:00:00 svs
1711 ? 00:00:00 udhcpc
1714 ? 00:00:00 dropbear
1715 pts/0 00:00:00 sh
1725 pts/0 00:00:00 ps
root@compulab-pxa270:~$
-
To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
