[PATCH] serial: 8250, increase PASS_LIMIT

[PATCH] serial: 8250, increase PASS_LIMIT

[Jiri Slaby]

From: Jiri Slaby <jirislaby@gmail.com>

With virtual machines like qemu, it's pretty common to see "too much
work for irq4" messages nowadays. This happens when a bunch of output
is printed on the emulated serial console. This is caused by too low
PASS_LIMIT. When ISR loops more than the limit, it spits the message.

I've been using a kernel with doubled the limit and I couldn't see no
problems. Maybe it's time to get rid of the message now?

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Cc: Alan Cox <alan@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
---
 drivers/tty/serial/8250.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/tty/serial/8250.c b/drivers/tty/serial/8250.c
index 54482d7..ae477c8 100644
--- a/drivers/tty/serial/8250.c
+++ b/drivers/tty/serial/8250.c
@@ -81,7 +81,7 @@ static unsigned int skip_txen_test; /* force skip of txen test at init time */
 #define DEBUG_INTR(fmt...)	do { } while (0)
 #endif
 
-#define PASS_LIMIT	256
+#define PASS_LIMIT	512
 
 #define BOTH_EMPTY 	(UART_LSR_TEMT | UART_LSR_THRE)
 
-- 
1.7.5.3

Re: [PATCH] serial: 8250, increase PASS_LIMIT

[Alan Cox]

On Sun,  5 Jun 2011 22:51:49 +0200
Jiri Slaby <jslaby@suse.cz> wrote:

> From: Jiri Slaby <jirislaby@gmail.com>
> 
> With virtual machines like qemu, it's pretty common to see "too much
> work for irq4" messages nowadays. This happens when a bunch of output
> is printed on the emulated serial console. This is caused by too low
> PASS_LIMIT. When ISR loops more than the limit, it spits the message.
> 
> I've been using a kernel with doubled the limit and I couldn't see no
> problems. Maybe it's time to get rid of the message now?

We need a limit to deal with hangs caused by misconfiguration /
mis-detection on ISA ports in particular but we can certainly bump the
limit to handle poor emulations.

Re: [PATCH] serial: 8250, increase PASS_LIMIT

[Jiri Slaby]

On 06/06/2011 02:09 PM, Alan Cox wrote:
> On Sun,  5 Jun 2011 22:51:49 +0200
> Jiri Slaby <jslaby@suse.cz> wrote:
> 
>> From: Jiri Slaby <jirislaby@gmail.com>
>>
>> With virtual machines like qemu, it's pretty common to see "too much
>> work for irq4" messages nowadays. This happens when a bunch of output
>> is printed on the emulated serial console. This is caused by too low
>> PASS_LIMIT. When ISR loops more than the limit, it spits the message.
>>
>> I've been using a kernel with doubled the limit and I couldn't see no
>> problems. Maybe it's time to get rid of the message now?
> 
> We need a limit to deal with hangs caused by misconfiguration /
> mis-detection on ISA ports in particular but we can certainly bump the
> limit to handle poor emulations.

Yeah, I meant it that way (get rid of the message by bumping the limit
-- this patch).

thanks,
-- 
js
suse labs