Date: Wed, 29 Oct 2014 21:51:31 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Sabrina Dubroca <sd@queasysnail.net>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, jeffrey.t.kirsher@intel.com
Subject: Re: e1000_netpoll(): disable_irq() triggers might_sleep() on
 linux-next
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References: <20141029155620.GA4886@kria>
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 <alpine.DEB.2.11.1410291918060.5308@nanos>
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 <alpine.DEB.2.11.1410292046270.5308@nanos>
 <20141029195054.GH10501@worktop.programming.kicks-ass.net>
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On Wed, Oct 29, 2014 at 09:23:42PM +0100, Thomas Gleixner wrote:
> But at least it allows to mitigate the impact by making it conditional
> at a central point.
> 
> static inline void netpoll_lock(struct net_device *nd)
> {
> 	if (netpoll_active(nd))
> 		spin_lock(&nd->netpoll_lock);
> }

branch fail vs lock might be a toss on most machines, but if we're
hitting cold cachelines we loose big.

> and let the core code make sure that activation/deactivation of
> netpoll on a particular interface is serialized against the interrupt
> and netpoll calls.
> 
> Not sure if it's worth the trouble, but at least it allows to deal
> with it in the core instead of dealing with it on a per driver base.

Does multi-queue have one netdev per queue or does that need moar
logicz?
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