linux-kernel - Re: [BUG] local_softirq

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Date:	Wed, 23 May 2007 22:54:07 +0200 (CEST)
From:	Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	David Miller <davem@...emloft.net>,
	linux-kernel@...r.kernel.org
Subject: Re: [BUG] local_softirq_pending storm

On Mon, 21 May 2007, Heiko Carstens wrote:

> On Sun, May 20, 2007 at 09:29:49PM +0200, Thomas Gleixner wrote:
>> On Sun, 2007-05-20 at 21:18 +0200, Heiko Carstens wrote:
>>>>> Hmm, that's a different problem than the 0x22 which shows up on
>>>>> hyperthreading enabled P4 systems. Are you using plip ?
>>>>
>>>> No, after all it turned out that is caused by an IBM internal module.
>>>> Just ignore me, sorry for the noise :)
>>>
>>> Just in case you're interested: I just looked into it and it turned
>>> out that this module was calling netif_rx() from process context,
>>> just like plip. Changing it to netif_rx_ni() fixes it.
>>
>> Thanks, that's a good pointer. You should have cc'ed Dave Miller and the
>> guy who found this plip thingy. Care to resend ?
>
> No problem. Here we go, even though I doubt that netif_rx_ni() is what
> people want for plip. Dunno...

netif_rx_ni calls softirq synchronously, am I right? That would probably 
hurt plip. I can try it if someone will be interested in it, but I doubt 
it is good solution for any network interfaces except tun.

BTW. does in_interrupt() have high cost on some high-performance 
architectures? Would it be possible to just add if (!in_interrupt()) 
wakeup_softirqd(); to netif_rx()?

Mikulas
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