linux-kernel - Re: [PATCH] NOHZ: local_softirq

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Date:	Thu, 17 May 2007 12:52:11 +0200
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH] NOHZ: local_softirq_pending with tickless plip

On Wed, 2007-05-16 at 15:00 +0200, Mikulas Patocka wrote:
> Hi
> 
> On one of my machines with tickless kernel and plip I get messages :

I bet this is a machine a P4 with Hyperthreading enabled ?

> NOHZ: local_softirq_pending 08
> 
> always when using plip (on other machine with tickless kernel and plip I 
> get no errors). Thebug happens both on 2.6.21 and 2.6.22-rc1
> 
> This patch fixes that. Note that plip calls netif_rx neither from hardware 
> interrupt nor from ksoftirqd, so there is no one who would wake 
> ksoftirqd then. netif_tx calls only 
> __raise_softirq_irqoff(NET_RX_SOFTIRQ), which sets softirq bit, but 
> doesn't wake ksoftirqd.

Dave, 

can we please get rid of __raise_softirq_irqoff() at all ? These micro
optimizations are causing more trouble than they are worth.

	tglx

> Mikulas
> 
> Signed-off-by: Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz
> 
> --- linux-2.6.22-rc1/net/core/dev.c_	Fri May 18 07:51:01 2007
> +++ linux-2.6.22-rc1/net/core/dev.c	Fri May 18 07:51:06 2007
> @@ -1117,7 +1117,7 @@
>   		dev->quota += dev->weight;
>   	else
>   		dev->quota = dev->weight;
> -	__raise_softirq_irqoff(NET_RX_SOFTIRQ);
> +	raise_softirq_irqoff(NET_RX_SOFTIRQ);
>   	local_irq_restore(flags);
>   }
>   EXPORT_SYMBOL(__netif_rx_schedule);


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