linux-kernel - Re: [PATCH 1/1] serial: 8250, disable "too much work" messages

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Message-ID: <s5hd2h1w77o.wl%tiwai@suse.de>
Date:	Tue, 01 Apr 2014 14:43:39 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	"Jiri Slaby" <jslaby@...e.cz>
Cc:	<gregkh@...uxfoundation.org>, <linux-kernel@...r.kernel.org>,
	<linux-serial@...r.kernel.org>
Subject: Re: [PATCH 1/1] serial: 8250, disable "too much work" messages

At Tue,  1 Apr 2014 13:37:00 +0200,
Jiri Slaby wrote:
> 
> The 8250 driver now reports many of these:
>   serial8250: too much work for irq4
> These messages turned out to be common these days with a use of
> virtualization. I tried to increase the limit of processed characters
> in commit e7328ae1848966181a7ac47e8ae6cddbd2cf55f3 (serial: 8250,
> increase PASS_LIMIT) in 2011. It was raised from 256 to 512, but it is
> still not enough, apparently.

Actually, it looks like a side-effect of the reduction of tasklet.  In
the earlier code, tty_wakeup() was called via tasklet, and this made
the loop in the interrupt handler finishing once.  Now it's called
directly, thus the irq handler may pick up more than before.

> So disable the warning unless somebody turns on DEBUG (or
> DYNAMIC_DEBUG _and_ the message).
> 
> Signed-off-by: Jiri Slaby <jslaby@...e.cz>
> Reported-by: Martin Pluskal <mpluskal@...e.com>
> Reported-by: Takashi Iwai <tiwai@...e.com>
> References: https://bugzilla.novell.com/show_bug.cgi?id=868394


In case it's still worth:
	Tested-by: Takashi Iwai <tiwai@...e.de>

thanks,

Takashi


> ---
>  drivers/tty/serial/8250/8250_core.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
> index 81f909c2101f..139ab1997e06 100644
> --- a/drivers/tty/serial/8250/8250_core.c
> +++ b/drivers/tty/serial/8250/8250_core.c
> @@ -1601,8 +1601,7 @@ static irqreturn_t serial8250_interrupt(int irq, void *dev_id)
>  		l = l->next;
>  
>  		if (l == i->head && pass_counter++ > PASS_LIMIT) {
> -			/* If we hit this, we're dead. */
> -			printk_ratelimited(KERN_ERR
> +			pr_debug_ratelimited(
>  				"serial8250: too much work for irq%d\n", irq);
>  			break;
>  		}
> -- 
> 1.9.1
> 
> 
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