linux-kernel - Re: [PATCH 1/1] via-rhine: Fix hanging with high CPU load on low-end broads.

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Date:	Wed, 28 Dec 2011 20:16:06 +0100
From:	Bjarke Istrup Pedersen <gurligebis@...too.org>
To:	David Miller <davem@...emloft.net>
Cc:	shemminger@...tta.com, bhutchings@...arflare.com,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	rl@...lgate.ch
Subject: Re: [PATCH 1/1] via-rhine: Fix hanging with high CPU load on low-end broads.

2011/12/28 David Miller <davem@...emloft.net>:
> From: Stephen Hemminger <shemminger@...tta.com>
> Date: Wed, 28 Dec 2011 10:17:10 -0800
>
>> Looks like the hardware isn't really disabling interrupts correctly to support
>> NAPI. NAPI is supposed to be friendly and under load the work should move to
>> ksoftirqd. I suspect the IRQ management in this driver is borked.
>> There is some stupid spin loops in the IRQ handler that happen when looking for
>> Tx IRQ. I would run with debug set  and see if this is triggering.
>
> This could be simply a side effect of the fact that via-rhine only does
> RX work in it's NAPI handler.
>
> If all the work (or at least both TX and RX) were moved into the NAPI
> handler, it'd probably be easier to properly shut off all IRQs during
> NAPI processing, and thus avoid the high CPU load in the IRQ handler
> being seen here.
>
> This "shut off only some interrupts" scheme is just asking for trouble.

I agree, it's an ugly hack :)

Is there some way I can help with this, without having to touch the
code? (C isn't my strong language, especially not kernel mode code) :)

/Bjarke

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