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

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Message-Id: <20070517.132937.29572252.davem@davemloft.net>
Date:	Thu, 17 May 2007 13:29:37 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	tglx@...utronix.de
Cc:	mikulas@...ax.karlin.mff.cuni.cz, mingo@...e.hu,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] NOHZ: local_softirq_pending with tickless plip

From: Thomas Gleixner <tglx@...utronix.de>
Date: Thu, 17 May 2007 12:52:11 +0200

> 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.

Actually I think this is pointing out a bug, in that plip is not
invoking things in the proper context, which will likely cause
other problems :-)

I'll put this on my TODO list and look into this.
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