losing interrupts - printk is bad

losing interrupts - printk is bad

[Matthias Fuchs]

Hi,

I got a nice problem: I am working on an embedded PPC board (IBM405CR)
with a serial console (115200 baud). While I was testing some new driver
code, I made a lot of prink debugging output - as we all like to do :-)
My problem is, that I always lose some bytes on an other serial port. I
found out that printk waits until the complete format string is send
through the console. That takes about 5 ms for 40 bytes. During this
time printk blocks the interrupts !!! That means some incomming data on
the other serial port can be (and is) lost. This is a very strange
problem.

Well first would be glad to get a good workaround. Well, a 'klogd -c 1'
turn off all the debuggin and printk is much faster, but I need the
debugging output.

Second, could anybody explain t ome, what klogd is doing ? It would be
glad to get klogd read all the debugging output from the kernel and
output the data from user space (well buffered and not blocking the
whole system). It seems that klogd cannot do that, am I right ?

Matthias

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Re: losing interrupts - printk is bad

[Gabriel Paubert]

On Mon, 19 Mar 2001, Matthias Fuchs wrote:

>
> Hi,
>
> I got a nice problem: I am working on an embedded PPC board (IBM405CR)
> with a serial console (115200 baud). While I was testing some new driver
> code, I made a lot of prink debugging output - as we all like to do :-)
> My problem is, that I always lose some bytes on an other serial port. I
> found out that printk waits until the complete format string is send
> through the console. That takes about 5 ms for 40 bytes. During this
> time printk blocks the interrupts !!! That means some incomming data on
> the other serial port can be (and is) lost. This is a very strange
> problem.
>
> Well first would be glad to get a good workaround. Well, a 'klogd -c 1'
> turn off all the debuggin and printk is much faster, but I need the
> debugging output.
>
> Second, could anybody explain t ome, what klogd is doing ? It would be
> glad to get klogd read all the debugging output from the kernel and
> output the data from user space (well buffered and not blocking the
> whole system). It seems that klogd cannot do that, am I right ?

Do you have a nettwork (Ethernet interface) ? I get all my debugging
output in /var/log/messages on another system with properly configured
syslogd. Of course, if has to go through userspace but once you've got
your driver stable enough , it should not be a problem.

	Regards,
	Gabriel.


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Re: losing interrupts - printk is bad

[Mike Neuhauser]

In message <3AB63E12.6D38973E@esd-electronics.com>, Matthias Fuchs writes:

  [stuff about losing interrupts during printk to serial console deleted]

> Second, could anybody explain t ome, what klogd is doing ? It would be
> glad to get klogd read all the debugging output from the kernel and
> output the data from user space (well buffered and not blocking the
> whole system). It seems that klogd cannot do that, am I right ?

klogd reads the kernel log messages (i.e. printk messages) either via syscall
or /proc interface and hands them over to syslogd.

Syslogd in turn writes them to a terminal, file, another host on
the network ...

So if you use klogd and syslogd together you can have kernel log message (also
on console if you like) and the other interrupts are not blocked by
printk.

Mike

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