netdev - Re: [net-next.git 3/8 (V2)] stmmac: add the initial tx coalesce schema

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Date:	Thu, 13 Sep 2012 21:42:51 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	David Miller <davem@...emloft.net>
CC:	<peppe.cavallaro@...com>, <netdev@...r.kernel.org>
Subject: Re: [net-next.git 3/8 (V2)] stmmac: add the initial tx coalesce
 schema

On Thu, 2012-09-13 at 16:23 -0400, David Miller wrote:
> From: Giuseppe CAVALLARO <peppe.cavallaro@...com>
> Date: Tue, 11 Sep 2012 08:55:09 +0200
> 
> > +	unsigned long flags;
> > +
> > +	spin_lock_irqsave(&priv->tx_lock, flags);
> >  
> > -	spin_lock(&priv->tx_lock);
> > +	priv->xstats.tx_clean++;
> 
> You are changing the locking here for the sake of the new timer.
> 
> But timers run in software interrupt context, so this change is
> completely unnecessary since NAPI runs in software interrupt context
> as well, and neither timers nor NAPI run in hardware interrupts
> context.

NAPI pollers can be called by netpoll in hardware interrupt context, and
this driver supports netpoll.

Ben.

> Therefore, disabling hardware interrupts for this lock is unnecessary
> and will decrease performance.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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