netdev - Re: e1000_netpoll(): disable_irq() triggers might

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Message-ID: <20141029205131.GI10501@worktop.programming.kicks-ass.net>
Date:	Wed, 29 Oct 2014 21:51:31 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Sabrina Dubroca <sd@...asysnail.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, jeffrey.t.kirsher@...el.com
Subject: Re: e1000_netpoll(): disable_irq() triggers might_sleep() on
 linux-next

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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