linux-kernel - Re: [patch 4/5] net: hip04: Make tx coalesce timer actually work

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Date:	Tue, 14 Apr 2015 00:08:23 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Arnd Bergmann <arnd@...db.de>
cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	dingtianhong <dingtianhong@...wei.com>,
	Zhangfei Gao <zhangfei.gao@...aro.org>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	netdev@...r.kernel.org
Subject: Re: [patch 4/5] net: hip04: Make tx coalesce timer actually work

On Tue, 14 Apr 2015, Arnd Bergmann wrote:
> On Monday 13 April 2015 23:42:03 Thomas Gleixner wrote:
> > > 
> > > Question: this looks to me like it sets both the minimum and maximum
> > > time to priv->tx_coalesce_usecs/2, when the intention was to set
> > > the minimum to priv->tx_coalesce_usecs/2 and the maximum to
> > > priv->tx_coalesce_usecs. Am I missing something subtle here, or did
> > > you just misread my original intention from the botched code?
> > 
> > Yes, I missed that. Simple fix for this is:
> > 
> >   unsigned long t_ns = priv->tx_coalesce_usecs * NSEC_PER_USEC / 2;
> >   
> >   hrtimer_start_range_ns(&priv->tx_coalesce_timer, ns_to_ktime(t_ns),
> >                          t_ns, HRTIMER_MODE_REL);
> 
> Ah, good. I have to admit that I'd probably make the same mistake
> again if I was to do this for another driver and you hadn't sent
> the fix. The hrtimer_set_expires_range() function just looked like
> it had been designed for the use case I was interested in ;-).
> 
> Any idea how to prevent the next person from making the same mistake?

Yes. Documentation :)

Thanks,

	tglx
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