Re: Serial stdio overwhelming interrupts

[Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>]

Liu Yu wrote:
> Hi guys,
>
> In my kvm machine, I use serial as its default stdio.
> But when display a number of characters, e.g. cat a big ascii file, 
> the serial always hangs as encount overwhelming interrupts, and then output a kernel log "serial8250: too much work for irq 42".
>
> I found that the serial in qemu is primitive so that it generate a interrupt on every single character. 
> This make it easier to reach the threshold of reporting "too much work".
>
> I had to use the patch below to get this issue walked arroud.
>
> Have you guys ever met the serial hanging problem before?
>   

We had that some times in the beginning while we brought up interrupts.
But since that time it did never occur again and I thought we fixed it.
Maybe your use case of catting a file to it is stressing it now to a new 
extend triggering it again.

> ---
> diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
> index be95e55..af3e569 100644
> --- a/drivers/serial/8250.c
> +++ b/drivers/serial/8250.c
> @@ -70,7 +70,7 @@ static unsigned int nr_uarts = CONFIG_SERIAL_8250_RUNTIME_UARTS;
>  #define DEBUG_INTR(fmt...)	do { } while (0)
>  #endif
>  
> -#define PASS_LIMIT	256
> +#define PASS_LIMIT	65535
>  
>  /*
>   * We default to IRQ0 for the "no irq" hack.   Some
>
> Best Regards.
>  
> Yu
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-- 

Grüsse / regards, 
Christian Ehrhardt
IBM Linux Technology Center, Open Virtualization