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

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Message-ID: <3040901.Bp3bfgc1te@wuerfel>
Date:	Tue, 14 Apr 2015 00:03:12 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Thomas Gleixner <tglx@...utronix.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 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?

	Arnd
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