netdev - Re: [PATCH 2.6.30-rc4] r8169: avoid losing MSI interrupts

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Date:	Tue, 25 Aug 2009 14:37:28 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	David Dillow <dave@...dillows.org>
Cc:	Michael Riepe <michael.riepe@...glemail.com>,
	Michael Buesch <mb@...sch.de>,
	Francois Romieu <romieu@...zoreil.com>,
	Rui Santos <rsantos@...popie.com>,
	Michael Büker <m.bueker@...lin.de>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 2.6.30-rc4] r8169: avoid losing MSI interrupts

David Dillow <dave@...dillows.org> writes:

> On Mon, 2009-08-24 at 17:51 -0700, Eric W. Biederman wrote:
>> When I decode the bits in status they are TxOK, RxOK and TxDescUnavail so it looks
>> there is some bidirectional communication going on.
>> 
>> Do we really want to loop when those bits are set?
>
> Maybe not when only those bits are set, but I worry that we would trade
> one race for another where we stop getting interrupts from the card.
>
>> Perhaps we want to remove them from rtl_cfg_infos for the part?
>
> Then you'd never get an interrupt for them in the first place, I think.
>
> I'm not real happy with the interrupt handling in the driver; it makes a
> certain amount of sense to split the MSI vs non-MSI interrupt cases out.
> It also means another pass through re-auditing things against the vendor
> driver. That's more work than I'm able to commit to at the moment.
>
> I've not been able to reproduce it locally on my r8169d, running for ~30
> minutes straight at full speed. I've not tried running it in UP, though.
> Perhaps I can do that tomorrow.
>
> Here's a possible patch to mask the NAPI events while we're running in
> NAPI mode. I'm not sure it is going to help, since the intr_mask was
> 0xffff when you hit the loop guard, so I left it in for now.

Ok.  I now get what your patch was trying to do and that does look like
a reasonable test.  

I prefer:
while ((status != 0xffff) && (status & tp->intr_mask))

The presence of TxDescUnavail suggests as is usually the case
that the interrupt status bits are independent of which interrupts
are actually enabled to fire.

I will take a moment and give that a try.

I still like the idea of masking everything having poll do all
of the work and then unmasking everything.  That seems a little less
fragile to me.

Eric

> diff --git a/drivers/net/r8169.c b/drivers/net/r8169.c
> index b82780d..12755b7 100644
> --- a/drivers/net/r8169.c
> +++ b/drivers/net/r8169.c
> @@ -3556,6 +3556,7 @@ static irqreturn_t rtl8169_interrupt(int irq, void *dev_instance)
>  	void __iomem *ioaddr = tp->mmio_addr;
>  	int handled = 0;
>  	int status;
> +	int count = 0;
>  
>  	/* loop handling interrupts until we have no new ones or
>  	 * we hit a invalid/hotplug case.
> @@ -3564,6 +3565,15 @@ static irqreturn_t rtl8169_interrupt(int irq, void *dev_instance)
>  	while (status && status != 0xffff) {
>  		handled = 1;
>  
> +		if (count++ > 100) {
> +			printk_once("r8169 screaming irq status %08x "
> +				"mask %08x event %08x napi %08x\n",
> +				status, tp->intr_mask, tp->intr_event,
> +				tp->napi_event);
> +			break;
> +		}
> +
> +
>  		/* Handle all of the error cases first. These will reset
>  		 * the chip, so just exit the loop.
>  		 */
> @@ -3613,6 +3623,7 @@ static irqreturn_t rtl8169_interrupt(int irq, void *dev_instance)
>  		RTL_W16(IntrStatus,
>  			(status & RxFIFOOver) ? (status | RxOverflow) : status);
>  		status = RTL_R16(IntrStatus);
> +		status &= tp->intr_mask;
>  	}
>  
>  	return IRQ_RETVAL(handled);
--
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